diff --git a/apps/desktop/app/hooks/export.ts b/apps/desktop/app/hooks/export.ts
new file mode 100644
index 0000000..7868ebd
--- /dev/null
+++ b/apps/desktop/app/hooks/export.ts
@@ -0,0 +1,20 @@
+import { useAdapter } from '~/hooks/useAdapter';
+import useSWRMutation from 'swr/mutation';
+
+interface ExportKey {
+  type: 'export';
+}
+
+/**
+ * プロジェクトをエクスポートする（保存ダイアログを含む）
+ */
+export function useExportProject() {
+  const adapter = useAdapter();
+  return useSWRMutation<undefined, Error, ExportKey, string>(
+    { type: 'export' },
+    async (_, { arg: projectId }) => {
+      await adapter.export.exportProject(projectId);
+      return undefined;
+    },
+  );
+}
diff --git a/apps/desktop/app/routes/(private)/home/page.tsx b/apps/desktop/app/routes/(private)/home/page.tsx
index 1644fdf..f27e0af 100644
--- a/apps/desktop/app/routes/(private)/home/page.tsx
+++ b/apps/desktop/app/routes/(private)/home/page.tsx
@@ -2,6 +2,7 @@ import { useState } from 'react';
 import { useNavigate, type MetaFunction } from 'react-router';
 import { useProjects, useCreateProject } from '~/hooks/projects';
 import { useLogout } from '~/hooks/auth';
+import { useExportProject } from '~/hooks/export';
 import {
   ProjectList,
   Button,
@@ -37,10 +38,14 @@ export default function Page() {
   const { data: projects, isLoading } = useProjects();
   const { trigger: createProject, isMutating: isCreating } = useCreateProject();
   const { trigger: logout, isMutating: isLoggingOut } = useLogout();
+  const { trigger: exportProject } = useExportProject();
 
   const [isCreateDialogOpen, setIsCreateDialogOpen] = useState(false);
   const [newProjectTitle, setNewProjectTitle] = useState('untitled');
   const [error, setError] = useState<string | null>(null);
+  const [exportingProjectId, setExportingProjectId] = useState<string | null>(
+    null,
+  );
 
   const defaultWorkDir = '~/TsumugiProjects';
 
@@ -73,6 +78,15 @@ export default function Page() {
     navigate(`${PATH_WORKSPACE}/${encodeURIComponent(project.id)}`);
   };
 
+  const handleExportProject = async (project: ProjectItem) => {
+    setExportingProjectId(project.id);
+    try {
+      await exportProject(project.id);
+    } finally {
+      setExportingProjectId(null);
+    }
+  };
+
   return (
     <div className="flex min-h-screen justify-center bg-background">
       <div className="flex-1 p-4 md:p-6">
@@ -122,6 +136,8 @@ export default function Page() {
                 projects={toProjectItems(projects)}
                 isLoading={isLoading}
                 onSelect={handleSelectProject}
+                onExport={handleExportProject}
+                exportingProjectId={exportingProjectId}
               />
             </div>
           </div>
diff --git a/apps/desktop/app/routes/(private)/workspace/[projectId]/_components/editors/project-editor-wrapper.tsx b/apps/desktop/app/routes/(private)/workspace/[projectId]/_components/editors/project-editor-wrapper.tsx
index 4143370..13bbf36 100644
--- a/apps/desktop/app/routes/(private)/workspace/[projectId]/_components/editors/project-editor-wrapper.tsx
+++ b/apps/desktop/app/routes/(private)/workspace/[projectId]/_components/editors/project-editor-wrapper.tsx
@@ -1,5 +1,6 @@
 import { useCallback } from 'react';
 import { useProject, useUpdateProject } from '~/hooks/projects';
+import { useExportProject } from '~/hooks/export';
 import { ProjectEditor, type ProjectEditorData } from '@tsumugi/ui';
 import { useDebouncedSave } from '~/routes/(private)/workspace/[projectId]/_hooks/useDebouncedSave';
 import type { Project } from '@tsumugi/adapter';
@@ -30,6 +31,8 @@ export function ProjectEditorWrapper({
 }: ProjectEditorWrapperProps) {
   const { data: project, mutate } = useProject(projectId, NO_REVALIDATE);
   const { trigger: updateProject } = useUpdateProject(projectId);
+  const { trigger: exportProject, isMutating: isExporting } =
+    useExportProject();
 
   const onSave = useCallback(
     async (field: string, value: unknown) => {
@@ -57,7 +60,18 @@ export function ProjectEditorWrapper({
     [mutate, debouncedSave, onNameChange],
   );
 
+  const handleExport = useCallback(async () => {
+    await exportProject(projectId);
+  }, [exportProject, projectId]);
+
   if (!project) return null;
 
-  return <ProjectEditor data={toEditorData(project)} onChange={handleChange} />;
+  return (
+    <ProjectEditor
+      data={toEditorData(project)}
+      onChange={handleChange}
+      onExport={handleExport}
+      isExporting={isExporting}
+    />
+  );
 }
diff --git a/package-lock.json b/package-lock.json
index 13b9499..96d7444 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -7989,9 +7989,9 @@
       }
     },
     "node_modules/@tsumugi-chan/client": {
-      "version": "1.0.7",
-      "resolved": "https://registry.npmjs.org/@tsumugi-chan/client/-/client-1.0.7.tgz",
-      "integrity": "sha512-BKRUZ5L4ggAfbbB5GsWryUmfQ5NYkGBwnFPCg1z2h9h+7c+t00xri5CWr2m3kM8HJye9CqmLVlEpWKD/qVCe9A==",
+      "version": "1.0.9",
+      "resolved": "https://registry.npmjs.org/@tsumugi-chan/client/-/client-1.0.9.tgz",
+      "integrity": "sha512-2fWAOuS282Cxt9Sp6igALsv66vPNgee5zlHeFyalzAG17tdl7Ey2S0K3jA7v2fZdDimias5cWJjcm6xRleV/Qw==",
       "license": "MIT"
     },
     "node_modules/@tsumugi/adapter": {
@@ -11962,6 +11962,12 @@
         "bser": "2.1.1"
       }
     },
+    "node_modules/fflate": {
+      "version": "0.8.2",
+      "resolved": "https://registry.npmjs.org/fflate/-/fflate-0.8.2.tgz",
+      "integrity": "sha512-cPJU47OaAoCbg0pBvzsgpTPhmhqI5eJjh/JIu8tPj5q+T7iLvW/JAYUqmE7KOB4R1ZyEhzBaIQpQpardBF5z8A==",
+      "license": "MIT"
+    },
     "node_modules/file-entry-cache": {
       "version": "8.0.0",
       "resolved": "https://registry.npmjs.org/file-entry-cache/-/file-entry-cache-8.0.0.tgz",
@@ -22476,7 +22482,7 @@
       "version": "0.0.1",
       "license": "UNLICENSED",
       "dependencies": {
-        "@tsumugi-chan/client": "1.0.7",
+        "@tsumugi-chan/client": "1.0.9",
         "@tsumugi/adapter": "*"
       },
       "devDependencies": {
@@ -22497,6 +22503,7 @@
         "@ai-sdk/openai": "3.0.30",
         "@tsumugi/adapter": "*",
         "ai": "6.0.94",
+        "fflate": "0.8.2",
         "zod": "4.3.6"
       },
       "devDependencies": {
diff --git a/packages/adapter/api/package.json b/packages/adapter/api/package.json
index c72c4df..d519422 100644
--- a/packages/adapter/api/package.json
+++ b/packages/adapter/api/package.json
@@ -35,7 +35,7 @@
     "test": "TZ=Asia/Tokyo jest"
   },
   "dependencies": {
-    "@tsumugi-chan/client": "1.0.7",
+    "@tsumugi-chan/client": "1.0.9",
     "@tsumugi/adapter": "*"
   },
   "devDependencies": {
diff --git a/packages/adapter/api/src/adapter.ts b/packages/adapter/api/src/adapter.ts
index 1d7941d..0253002 100644
--- a/packages/adapter/api/src/adapter.ts
+++ b/packages/adapter/api/src/adapter.ts
@@ -8,6 +8,7 @@ import { createMemoAdapter } from '@/adapters/memo';
 import { createWritingAdapter } from '@/adapters/writing';
 import { createSettingsAdapter } from '@/adapters/settings';
 import { createAIAdapter } from '@/adapters/ai';
+import { createExportAdapter } from '@/adapters/export';
 import { TokenManager } from '@/token-manager';
 
 export function createAdapter(config: AdapterConfig = {}): Adapter {
@@ -33,5 +34,6 @@ export function createAdapter(config: AdapterConfig = {}): Adapter {
     memos: createMemoAdapter(clients),
     writings: createWritingAdapter(clients),
     ai: createAIAdapter(clients),
+    export: createExportAdapter(clients),
   };
 }
diff --git a/packages/adapter/api/src/adapters/export.ts b/packages/adapter/api/src/adapters/export.ts
new file mode 100644
index 0000000..341a32b
--- /dev/null
+++ b/packages/adapter/api/src/adapters/export.ts
@@ -0,0 +1,38 @@
+import type { ExportAdapter, ExportOptions } from '@tsumugi/adapter';
+import type { ApiClients } from '@/client';
+
+function triggerBrowserDownload(blob: Blob, filename: string): void {
+  const url = URL.createObjectURL(blob);
+  const a = document.createElement('a');
+  a.href = url;
+  a.download = filename;
+  document.body.appendChild(a);
+  a.click();
+  document.body.removeChild(a);
+  URL.revokeObjectURL(url);
+}
+
+function extractFilename(headers: Headers): string {
+  const disposition = headers.get('Content-Disposition');
+  if (disposition) {
+    const rfcMatch = disposition.match(/filename\*=UTF-8''([^;]+)/i);
+    if (rfcMatch) return decodeURIComponent(rfcMatch[1]);
+    const match = disposition.match(/filename="?([^";\n]+)"?/i);
+    if (match) return match[1].trim();
+  }
+  return 'export.zip';
+}
+
+export function createExportAdapter(clients: ApiClients): ExportAdapter {
+  return {
+    async exportProject(
+      projectId: string,
+      _options?: ExportOptions,
+    ): Promise<void> {
+      const response = await clients.projects.exportProjectRaw({ projectId });
+      const blob = await response.raw.blob();
+      const filename = extractFilename(response.raw.headers);
+      triggerBrowserDownload(blob, filename);
+    },
+  };
+}
diff --git a/packages/adapter/api/tsconfig.json b/packages/adapter/api/tsconfig.json
index 9f7c982..a44dc0e 100644
--- a/packages/adapter/api/tsconfig.json
+++ b/packages/adapter/api/tsconfig.json
@@ -1,7 +1,7 @@
 {
   "compilerOptions": {
     "target": "ES2020",
-    "lib": ["ES2020"],
+    "lib": ["ES2020", "DOM"],
     "module": "ESNext",
     "moduleResolution": "bundler",
     "strict": true,
diff --git a/packages/adapter/core/src/adapter.ts b/packages/adapter/core/src/adapter.ts
index 46bd25f..266e515 100644
--- a/packages/adapter/core/src/adapter.ts
+++ b/packages/adapter/core/src/adapter.ts
@@ -17,6 +17,7 @@ import type {
   AIProjectUsage,
   AuthState,
   GoogleAuthUrl,
+  ExportOptions,
 } from './types';
 
 /**
@@ -243,6 +244,18 @@ export interface AuthAdapter {
   refreshAccessToken(): Promise<AuthState>;
 }
 
+/**
+ * エクスポート操作のインターフェース
+ */
+export interface ExportAdapter {
+  /**
+   * プロジェクトをエクスポート
+   * @param projectId - エクスポートするプロジェクトID
+   * @param options - エクスポートオプション（省略時はすべてのコンテンツを zip-markdown でエクスポート）
+   */
+  exportProject(projectId: string, options?: ExportOptions): Promise<void>;
+}
+
 /**
  * 統合アダプター
  */
@@ -255,4 +268,5 @@ export interface Adapter {
   readonly memos: MemoAdapter;
   readonly writings: WritingAdapter;
   readonly ai: AIAdapter;
+  readonly export: ExportAdapter;
 }
diff --git a/packages/adapter/core/src/stub.ts b/packages/adapter/core/src/stub.ts
index 09c36b3..e205c6f 100644
--- a/packages/adapter/core/src/stub.ts
+++ b/packages/adapter/core/src/stub.ts
@@ -92,5 +92,8 @@ export function createAdapter(_: AdapterConfig = {}): Adapter {
       deleteMemory: () => notImplemented(),
       getUsage: () => notImplemented(),
     },
+    export: {
+      exportProject: () => notImplemented(),
+    },
   };
 }
diff --git a/packages/adapter/core/src/types.ts b/packages/adapter/core/src/types.ts
index 519b291..2d6e3e2 100644
--- a/packages/adapter/core/src/types.ts
+++ b/packages/adapter/core/src/types.ts
@@ -507,3 +507,24 @@ export interface GoogleAuthUrl {
   /** Google OAuth認可URL */
   url: string;
 }
+
+/**
+ * エクスポートのフォーマット
+ */
+export type ExportFormat = 'zip-markdown';
+
+/**
+ * エクスポートオプション
+ */
+export interface ExportOptions {
+  /** エクスポートフォーマット（デフォルト: 'zip-markdown'） */
+  format?: ExportFormat;
+  /** 執筆データを含めるか（デフォルト: true） */
+  includeWritings?: boolean;
+  /** プロットデータを含めるか（デフォルト: true） */
+  includePlots?: boolean;
+  /** キャラクターデータを含めるか（デフォルト: true） */
+  includeCharacters?: boolean;
+  /** メモデータを含めるか（デフォルト: true） */
+  includeMemos?: boolean;
+}
diff --git a/packages/adapter/local/package.json b/packages/adapter/local/package.json
index 04a0f1c..a00ab04 100644
--- a/packages/adapter/local/package.json
+++ b/packages/adapter/local/package.json
@@ -39,6 +39,7 @@
     "@ai-sdk/openai": "3.0.30",
     "@tsumugi/adapter": "*",
     "ai": "6.0.94",
+    "fflate": "0.8.2",
     "zod": "4.3.6"
   },
   "peerDependencies": {
diff --git a/packages/adapter/local/src/adapter.ts b/packages/adapter/local/src/adapter.ts
index 155d0b3..ce6fd14 100644
--- a/packages/adapter/local/src/adapter.ts
+++ b/packages/adapter/local/src/adapter.ts
@@ -7,6 +7,7 @@ import { createMemoAdapter } from '@/adapters/memo';
 import { createWritingAdapter } from '@/adapters/writing';
 import { createAIAdapter } from '@/adapters/ai';
 import { createSettingsAdapter } from '@/adapters/settings';
+import { createExportAdapter } from '@/adapters/export';
 
 export function createAdapter(config: AdapterConfig = {}): Adapter {
   const workDir = config.local?.workDir;
@@ -32,5 +33,12 @@ export function createAdapter(config: AdapterConfig = {}): Adapter {
       memos,
       writings,
     }),
+    export: createExportAdapter({
+      projects,
+      plots,
+      characters,
+      memos,
+      writings,
+    }),
   };
 }
diff --git a/packages/adapter/local/src/adapters/export.ts b/packages/adapter/local/src/adapters/export.ts
new file mode 100644
index 0000000..7d92bcb
--- /dev/null
+++ b/packages/adapter/local/src/adapters/export.ts
@@ -0,0 +1,92 @@
+import type {
+  ExportAdapter,
+  ExportOptions,
+  ProjectAdapter,
+  WritingAdapter,
+  PlotAdapter,
+  CharacterAdapter,
+  MemoAdapter,
+} from '@tsumugi/adapter';
+import { zipSync, strToU8 } from 'fflate';
+import { save } from '@tauri-apps/plugin-dialog';
+import {
+  sanitizeFileName,
+  buildProjectReadme,
+  buildWritingEntries,
+  buildPlotEntries,
+  buildCharacterEntries,
+  buildMemoEntries,
+  type ZipEntry,
+} from '@/internal/utils/export-markdown';
+import { writeBinaryFile } from '@/internal/utils/fs';
+
+export interface ExportAdapterDeps {
+  projects: ProjectAdapter;
+  writings: WritingAdapter;
+  plots: PlotAdapter;
+  characters: CharacterAdapter;
+  memos: MemoAdapter;
+}
+
+export function createExportAdapter(deps: ExportAdapterDeps): ExportAdapter {
+  const { projects, writings, plots, characters, memos } = deps;
+
+  return {
+    async exportProject(
+      projectId: string,
+      options: ExportOptions = {},
+    ): Promise<void> {
+      const {
+        includeWritings = true,
+        includePlots = true,
+        includeCharacters = true,
+        includeMemos = true,
+      } = options;
+
+      const project = await projects.getById(projectId);
+      if (!project) throw new Error(`Project not found: ${projectId}`);
+
+      const entries: ZipEntry[] = [
+        { path: 'README.md', content: buildProjectReadme(project) },
+      ];
+
+      if (includeWritings) {
+        const ws = await writings.getByProjectId(projectId);
+        entries.push(...buildWritingEntries(ws));
+      }
+
+      if (includePlots) {
+        const ps = await plots.getByProjectId(projectId);
+        entries.push(...buildPlotEntries(ps));
+      }
+
+      if (includeCharacters) {
+        const cs = await characters.getByProjectId(projectId);
+        entries.push(...buildCharacterEntries(cs));
+      }
+
+      if (includeMemos) {
+        const ms = await memos.getByProjectId(projectId);
+        entries.push(...buildMemoEntries(ms));
+      }
+
+      const projectSlug = sanitizeFileName(project.name);
+
+      const zipFiles: Record<string, Uint8Array> = {};
+      for (const entry of entries) {
+        zipFiles[`${projectSlug}/${entry.path}`] = strToU8(entry.content);
+      }
+
+      const data = zipSync(zipFiles);
+      const filename = `${projectSlug}-export.zip`;
+
+      const savePath = await save({
+        defaultPath: filename,
+        filters: [{ name: 'ZIP', extensions: ['zip'] }],
+      });
+      if (!savePath) return;
+
+      await writeBinaryFile(savePath, data);
+    },
+  };
+}
diff --git a/packages/adapter/local/src/internal/utils/export-markdown.spec.ts b/packages/adapter/local/src/internal/utils/export-markdown.spec.ts
new file mode 100644
index 0000000..afa519d
--- /dev/null
+++ b/packages/adapter/local/src/internal/utils/export-markdown.spec.ts
@@ -0,0 +1,483 @@
+import type { Project, Writing, Plot, Character, Memo } from '@tsumugi/adapter';
+import {
+  sanitizeFileName,
+  formatOrder,
+  buildSegment,
+  buildProjectReadme,
+  buildWritingMarkdown,
+  buildPlotMarkdown,
+  buildCharacterMarkdown,
+  buildMemoMarkdown,
+  buildWritingEntries,
+  buildPlotEntries,
+  buildCharacterEntries,
+  buildMemoEntries,
+} from './export-markdown';
+
+const baseTimestamps = {
+  createdAt: new Date('2024-01-01'),
+  updatedAt: new Date('2024-01-02'),
+};
+
+const baseNode = {
+  projectId: '/projects/test',
+  parentId: null,
+  ...baseTimestamps,
+};
+
+function makeWriting(
+  overrides: Partial<Writing> & Pick<Writing, 'id' | 'name' | 'order'>,
+): Writing {
+  return {
+    ...baseNode,
+    nodeType: 'writing',
+    parentId: null,
+    content: '',
+    wordCount: 0,
+    ...overrides,
+  };
+}
+
+function makePlot(
+  overrides: Partial<Plot> & Pick<Plot, 'id' | 'name' | 'order'>,
+): Plot {
+  return {
+    ...baseNode,
+    nodeType: 'plot',
+    parentId: null,
+    ...overrides,
+  };
+}
+
+function makeCharacter(
+  overrides: Partial<Character> & Pick<Character, 'id' | 'name' | 'order'>,
+): Character {
+  return {
+    ...baseNode,
+    nodeType: 'character',
+    parentId: null,
+    ...overrides,
+  };
+}
+
+function makeMemo(
+  overrides: Partial<Memo> & Pick<Memo, 'id' | 'name' | 'order'>,
+): Memo {
+  return {
+    ...baseNode,
+    nodeType: 'memo',
+    parentId: null,
+    content: '',
+    ...overrides,
+  };
+}
+
+// ---------------------------------------------------------------------------
+// sanitizeFileName
+// ---------------------------------------------------------------------------
+
+describe('sanitizeFileName', () => {
+  it('通常の文字列はそのまま返す', () => {
+    expect(sanitizeFileName('第一章')).toBe('第一章');
+  });
+
+  it('スラッシュをハイフンに変換する', () => {
+    expect(sanitizeFileName('act/scene')).toBe('act-scene');
+  });
+
+  it('バックスラッシュをハイフンに変換する', () => {
+    expect(sanitizeFileName('act\\scene')).toBe('act-scene');
+  });
+
+  it('コロン等の特殊文字をハイフンに変換する', () => {
+    // スペースはそのまま保持、コロンのみハイフンに変換される
+    expect(sanitizeFileName('chapter: one')).toBe('chapter- one');
+    // 連続する特殊文字は1つのハイフンにまとめる
+    expect(sanitizeFileName('chapter::one')).toBe('chapter-one');
+  });
+
+  it('先頭・末尾のハイフンを除去する', () => {
+    expect(sanitizeFileName('/chapter/')).toBe('chapter');
+  });
+
+  it('空文字列は untitled を返す', () => {
+    expect(sanitizeFileName('')).toBe('untitled');
+  });
+
+  it('特殊文字のみは untitled を返す', () => {
+    expect(sanitizeFileName('///')).toBe('untitled');
+  });
+});
+
+// ---------------------------------------------------------------------------
+// formatOrder
+// ---------------------------------------------------------------------------
+
+describe('formatOrder', () => {
+  it('0 は "0000" になる', () => {
+    expect(formatOrder(0)).toBe('0000');
+  });
+
+  it('42 は "0042" になる', () => {
+    expect(formatOrder(42)).toBe('0042');
+  });
+
+  it('9999 は "9999" になる', () => {
+    expect(formatOrder(9999)).toBe('9999');
+  });
+
+  it('10000 は 5桁になる（パディングは最低桁数のみ保証）', () => {
+    expect(formatOrder(10000)).toBe('10000');
+  });
+});
+
+// ---------------------------------------------------------------------------
+// buildSegment
+// ---------------------------------------------------------------------------
+
+describe('buildSegment', () => {
+  it('order と name を結合したセグメントを返す', () => {
+    expect(buildSegment(0, '第一章')).toBe('0000_第一章');
+    expect(buildSegment(3, 'プロローグ')).toBe('0003_プロローグ');
+  });
+
+  it('name に特殊文字が含まれる場合はサニタイズする', () => {
+    expect(buildSegment(1, 'act/scene')).toBe('0001_act-scene');
+  });
+});
+
+// ---------------------------------------------------------------------------
+// buildProjectReadme
+// ---------------------------------------------------------------------------
+
+describe('buildProjectReadme', () => {
+  const baseProject: Project = {
+    id: '/projects/test',
+    name: 'テストプロジェクト',
+    ...baseTimestamps,
+  };
+
+  it('name のみのプロジェクトは h1 タイトルと空行を返す', () => {
+    const result = buildProjectReadme(baseProject);
+    expect(result).toBe('# テストプロジェクト\n');
+  });
+
+  it('synopsis があればセクションを含む', () => {
+    const project: Project = { ...baseProject, synopsis: 'あらすじ内容' };
+    const result = buildProjectReadme(project);
+    expect(result).toContain('## あらすじ');
+    expect(result).toContain('あらすじ内容');
+  });
+
+  it('theme, goal, targetWordCount, targetAudience が全てある場合', () => {
+    const project: Project = {
+      ...baseProject,
+      synopsis: 'あらすじ',
+      theme: 'テーマ',
+      goal: 'ゴール',
+      targetWordCount: 80000,
+      targetAudience: '一般',
+    };
+    const result = buildProjectReadme(project);
+    expect(result).toContain('## テーマ');
+    expect(result).toContain('## ゴール');
+    expect(result).toContain('## 目標文字数');
+    expect(result).toContain('80000');
+    expect(result).toContain('## 対象読者');
+    expect(result).toContain('一般');
+  });
+});
+
+// ---------------------------------------------------------------------------
+// buildWritingMarkdown
+// ---------------------------------------------------------------------------
+
+describe('buildWritingMarkdown', () => {
+  it('name と content を含む markdown を生成する', () => {
+    const writing = makeWriting({
+      id: '/writings/1.json',
+      name: 'プロローグ',
+      order: 0,
+      content: '物語のはじまり。',
+    });
+    const result = buildWritingMarkdown(writing);
+    expect(result).toBe('# プロローグ\n\n物語のはじまり。');
+  });
+
+  it('content が空の場合は h1 のみ', () => {
+    const writing = makeWriting({
+      id: '/writings/1.json',
+      name: '空の章',
+      order: 0,
+    });
+    const result = buildWritingMarkdown(writing);
+    expect(result).toBe('# 空の章\n');
+  });
+});
+
+// ---------------------------------------------------------------------------
+// buildPlotMarkdown
+// ---------------------------------------------------------------------------
+
+describe('buildPlotMarkdown', () => {
+  it('全フィールドがある場合は全セクションを含む', () => {
+    const plot = makePlot({
+      id: '/plots/1.json',
+      name: 'メインプロット',
+      order: 0,
+      synopsis: 'あらすじ',
+      setting: '舞台設定',
+      theme: 'テーマ',
+      structure: '三幕構成',
+      conflict: '主人公 vs 敵',
+      resolution: 'ハッピーエンド',
+      notes: 'メモ',
+    });
+    const result = buildPlotMarkdown(plot);
+    expect(result).toContain('# メインプロット');
+    expect(result).toContain('## あらすじ');
+    expect(result).toContain('## 舞台設定');
+    expect(result).toContain('## テーマ');
+    expect(result).toContain('## 構成');
+    expect(result).toContain('## 葛藤');
+    expect(result).toContain('## 解決');
+    expect(result).toContain('## ノート');
+  });
+
+  it('フィールドが空の場合はそのセクションを省略する', () => {
+    const plot = makePlot({
+      id: '/plots/1.json',
+      name: 'シンプルプロット',
+      order: 0,
+    });
+    const result = buildPlotMarkdown(plot);
+    expect(result).not.toContain('## あらすじ');
+  });
+});
+
+// ---------------------------------------------------------------------------
+// buildCharacterMarkdown
+// ---------------------------------------------------------------------------
+
+describe('buildCharacterMarkdown', () => {
+  it('基本情報がある場合はテーブルを含む', () => {
+    const character = makeCharacter({
+      id: '/characters/1.json',
+      name: '主人公',
+      order: 0,
+      role: '探偵',
+      gender: '男性',
+      age: '30',
+      aliases: 'Mr.X',
+    });
+    const result = buildCharacterMarkdown(character);
+    expect(result).toContain('| 項目 | 内容 |');
+    expect(result).toContain('| 役割 | 探偵 |');
+    expect(result).toContain('| 性別 | 男性 |');
+    expect(result).toContain('| 年齢 | 30 |');
+    expect(result).toContain('| 別名 | Mr.X |');
+  });
+
+  it('基本情報が全てない場合はテーブルを省略する', () => {
+    const character = makeCharacter({
+      id: '/characters/1.json',
+      name: '謎の人物',
+      order: 0,
+    });
+    const result = buildCharacterMarkdown(character);
+    expect(result).not.toContain('| 項目 | 内容 |');
+  });
+
+  it('詳細フィールドがある場合はセクションを含む', () => {
+    const character = makeCharacter({
+      id: '/characters/1.json',
+      name: '主人公',
+      order: 0,
+      appearance: '黒髪',
+      personality: '誠実',
+      background: '幼少期に孤独',
+      motivation: '真実を追う',
+      relationships: '相棒がいる',
+      notes: '補足',
+    });
+    const result = buildCharacterMarkdown(character);
+    expect(result).toContain('## 外見');
+    expect(result).toContain('## 性格');
+    expect(result).toContain('## 背景');
+    expect(result).toContain('## 動機');
+    expect(result).toContain('## 人間関係');
+    expect(result).toContain('## ノート');
+  });
+});
+
+// ---------------------------------------------------------------------------
+// buildMemoMarkdown
+// ---------------------------------------------------------------------------
+
+describe('buildMemoMarkdown', () => {
+  it('タグありのメモを正しく出力する', () => {
+    const memo = makeMemo({
+      id: '/memos/1.json',
+      name: '設定メモ',
+      order: 0,
+      content: '世界観の説明。',
+      tags: ['設定', '世界観'],
+    });
+    const result = buildMemoMarkdown(memo);
+    expect(result).toContain('# 設定メモ');
+    expect(result).toContain('タグ: 設定, 世界観');
+    expect(result).toContain('世界観の説明。');
+  });
+
+  it('タグなしのメモはタグ行を省略する', () => {
+    const memo = makeMemo({
+      id: '/memos/1.json',
+      name: 'タグなし',
+      order: 0,
+      content: 'メモ内容',
+    });
+    const result = buildMemoMarkdown(memo);
+    expect(result).not.toContain('タグ:');
+  });
+});
+
+// ---------------------------------------------------------------------------
+// buildWritingEntries（ツリー構造）
+// ---------------------------------------------------------------------------
+
+describe('buildWritingEntries', () => {
+  it('フラットなリストから zip パスを正しく生成する', () => {
+    const writings: Writing[] = [
+      makeWriting({ id: 'id-1', name: 'プロローグ', order: 0 }),
+      makeWriting({ id: 'id-2', name: 'エピローグ', order: 1 }),
+    ];
+    const entries = buildWritingEntries(writings);
+    expect(entries).toHaveLength(2);
+    expect(entries[0].path).toBe('writings/0000_プロローグ.md');
+    expect(entries[1].path).toBe('writings/0001_エピローグ.md');
+  });
+
+  it('フォルダノードは除外する', () => {
+    const writings: Writing[] = [
+      makeWriting({
+        id: 'folder-1',
+        name: '第一部',
+        order: 0,
+        nodeType: 'folder',
+        content: '',
+      }),
+      makeWriting({
+        id: 'id-1',
+        name: '第一章',
+        order: 0,
+        parentId: 'folder-1',
+      }),
+    ];
+    const entries = buildWritingEntries(writings);
+    expect(entries).toHaveLength(1);
+    expect(entries[0].path).toBe('writings/0000_第一部/0000_第一章.md');
+  });
+
+  it('ネストしたフォルダ構造でパスが正しく生成される', () => {
+    const writings: Writing[] = [
+      makeWriting({
+        id: 'folder-1',
+        name: '第一部',
+        order: 0,
+        nodeType: 'folder',
+        content: '',
+      }),
+      makeWriting({
+        id: 'folder-2',
+        name: '前半',
+        order: 0,
+        nodeType: 'folder',
+        content: '',
+        parentId: 'folder-1',
+      }),
+      makeWriting({
+        id: 'id-1',
+        name: '第一章',
+        order: 0,
+        parentId: 'folder-2',
+      }),
+    ];
+    const entries = buildWritingEntries(writings);
+    expect(entries).toHaveLength(1);
+    expect(entries[0].path).toBe(
+      'writings/0000_第一部/0000_前半/0000_第一章.md',
+    );
+  });
+
+  it('親が見つからない孤立ノードはルートに配置される', () => {
+    const writings: Writing[] = [
+      makeWriting({
+        id: 'id-1',
+        name: '孤立した章',
+        order: 2,
+        parentId: 'non-existent',
+      }),
+    ];
+    const entries = buildWritingEntries(writings);
+    expect(entries).toHaveLength(1);
+    expect(entries[0].path).toBe('writings/0002_孤立した章.md');
+  });
+});
+
+// ---------------------------------------------------------------------------
+// buildPlotEntries
+// ---------------------------------------------------------------------------
+
+describe('buildPlotEntries', () => {
+  it('フォルダを除外しプロット一覧の zip パスを生成する', () => {
+    const plots: Plot[] = [
+      makePlot({
+        id: 'folder-1',
+        name: 'グループ',
+        order: 0,
+        nodeType: 'folder',
+      }),
+      makePlot({
+        id: 'id-1',
+        name: 'メインプロット',
+        order: 0,
+        parentId: 'folder-1',
+      }),
+    ];
+    const entries = buildPlotEntries(plots);
+    expect(entries).toHaveLength(1);
+    expect(entries[0].path).toBe('plots/0000_グループ/0000_メインプロット.md');
+  });
+});
+
+// ---------------------------------------------------------------------------
+// buildCharacterEntries
+// ---------------------------------------------------------------------------
+
+describe('buildCharacterEntries', () => {
+  it('フォルダを除外しキャラクター一覧の zip パスを生成する', () => {
+    const characters: Character[] = [
+      makeCharacter({ id: 'id-1', name: '主人公', order: 0 }),
+      makeCharacter({ id: 'id-2', name: '敵役', order: 1 }),
+    ];
+    const entries = buildCharacterEntries(characters);
+    expect(entries).toHaveLength(2);
+    expect(entries[0].path).toBe('characters/0000_主人公.md');
+    expect(entries[1].path).toBe('characters/0001_敵役.md');
+  });
+});
+
+// ---------------------------------------------------------------------------
+// buildMemoEntries
+// ---------------------------------------------------------------------------
+
+describe('buildMemoEntries', () => {
+  it('フォルダを除外しメモ一覧の zip パスを生成する', () => {
+    const memos: Memo[] = [
+      makeMemo({ id: 'id-1', name: '設定メモ', order: 0, tags: ['設定'] }),
+    ];
+    const entries = buildMemoEntries(memos);
+    expect(entries).toHaveLength(1);
+    expect(entries[0].path).toBe('memos/0000_設定メモ.md');
+  });
+});
diff --git a/packages/adapter/local/src/internal/utils/export-markdown.ts b/packages/adapter/local/src/internal/utils/export-markdown.ts
new file mode 100644
index 0000000..2c47e40
--- /dev/null
+++ b/packages/adapter/local/src/internal/utils/export-markdown.ts
@@ -0,0 +1,189 @@
+import type {
+  Project,
+  Writing,
+  Plot,
+  Character,
+  Memo,
+  Node,
+} from '@tsumugi/adapter';
+
+export interface ZipEntry {
+  /** zip 内のパス（プロジェクト名ディレクトリより下の相対パス） */
+  path: string;
+  content: string;
+}
+
+/**
+ * ファイルシステムで安全なファイル名に変換する。
+ * スラッシュ等の特殊文字は `-` に置換し、連続する `-` はまとめる。
+ */
+export function sanitizeFileName(name: string): string {
+  return (
+    name
+      .replace(/[/\\:*?"<>|]/g, '-')
+      .replace(/-+/g, '-')
+      .replace(/^-|-$/g, '')
+      .trim() || 'untitled'
+  );
+}
+
+/**
+ * order を4桁ゼロパディングでフォーマットする。
+ * 例: 0 → "0000", 42 → "0042"
+ */
+export function formatOrder(order: number): string {
+  return String(order).padStart(4, '0');
+}
+
+/**
+ * ノードのパスセグメントを生成する（拡張子なし）。
+ * 例: order=3, name="第一章" → "0003_第一章"
+ */
+export function buildSegment(order: number, name: string): string {
+  return `${formatOrder(order)}_${sanitizeFileName(name)}`;
+}
+
+/**
+ * ノードの zip パスを再帰的に計算する（拡張子なし）。
+ * 親ノードが存在する場合はそのパスをプレフィックスとして結合する。
+ */
+function getNodeZipPath(node: Node, nodeMap: Map<string, Node>): string {
+  const segment = buildSegment(node.order, node.name);
+  if (node.parentId === null) return segment;
+  const parent = nodeMap.get(node.parentId);
+  if (!parent) return segment;
+  return `${getNodeZipPath(parent, nodeMap)}/${segment}`;
+}
+
+/**
+ * プロジェクト概要の README.md コンテンツを生成する。
+ */
+export function buildProjectReadme(project: Project): string {
+  const lines: string[] = [`# ${project.name}`, ''];
+  if (project.synopsis) lines.push('## あらすじ', '', project.synopsis, '');
+  if (project.theme) lines.push('## テーマ', '', project.theme, '');
+  if (project.goal) lines.push('## ゴール', '', project.goal, '');
+  if (project.targetWordCount != null)
+    lines.push('## 目標文字数', '', String(project.targetWordCount), '');
+  if (project.targetAudience)
+    lines.push('## 対象読者', '', project.targetAudience, '');
+  return lines.join('\n');
+}
+
+/**
+ * Writing の markdown コンテンツを生成する。
+ */
+export function buildWritingMarkdown(writing: Writing): string {
+  const lines: string[] = [`# ${writing.name}`, ''];
+  if (writing.content) lines.push(writing.content);
+  return lines.join('\n');
+}
+
+/**
+ * Plot の markdown コンテンツを生成する。
+ */
+export function buildPlotMarkdown(plot: Plot): string {
+  const lines: string[] = [`# ${plot.name}`, ''];
+  if (plot.synopsis) lines.push('## あらすじ', '', plot.synopsis, '');
+  if (plot.setting) lines.push('## 舞台設定', '', plot.setting, '');
+  if (plot.theme) lines.push('## テーマ', '', plot.theme, '');
+  if (plot.structure) lines.push('## 構成', '', plot.structure, '');
+  if (plot.conflict) lines.push('## 葛藤', '', plot.conflict, '');
+  if (plot.resolution) lines.push('## 解決', '', plot.resolution, '');
+  if (plot.notes) lines.push('## ノート', '', plot.notes, '');
+  return lines.join('\n');
+}
+
+/**
+ * Character の markdown コンテンツを生成する。
+ * 基本情報はテーブル形式、詳細説明はセクション形式で出力する。
+ */
+export function buildCharacterMarkdown(character: Character): string {
+  const lines: string[] = [`# ${character.name}`, ''];
+
+  const tableRows: string[] = [];
+  if (character.role) tableRows.push(`| 役割 | ${character.role} |`);
+  if (character.gender) tableRows.push(`| 性別 | ${character.gender} |`);
+  if (character.age) tableRows.push(`| 年齢 | ${character.age} |`);
+  if (character.aliases) tableRows.push(`| 別名 | ${character.aliases} |`);
+
+  if (tableRows.length > 0) {
+    lines.push('| 項目 | 内容 |', '|------|------|', ...tableRows, '');
+  }
+
+  if (character.appearance) lines.push('## 外見', '', character.appearance, '');
+  if (character.personality)
+    lines.push('## 性格', '', character.personality, '');
+  if (character.background) lines.push('## 背景', '', character.background, '');
+  if (character.motivation) lines.push('## 動機', '', character.motivation, '');
+  if (character.relationships)
+    lines.push('## 人間関係', '', character.relationships, '');
+  if (character.notes) lines.push('## ノート', '', character.notes, '');
+
+  return lines.join('\n');
+}
+
+/**
+ * Memo の markdown コンテンツを生成する。
+ */
+export function buildMemoMarkdown(memo: Memo): string {
+  const lines: string[] = [`# ${memo.name}`, ''];
+  if (memo.tags && memo.tags.length > 0) {
+    lines.push(`タグ: ${memo.tags.join(', ')}`, '');
+  }
+  if (memo.content) lines.push(memo.content);
+  return lines.join('\n');
+}
+
+/**
+ * Writing のフラットリストから ZipEntry[] を生成する。
+ * フォルダノードは除外し、コンテンツノードのみ出力する。
+ */
+export function buildWritingEntries(writings: Writing[]): ZipEntry[] {
+  const nodeMap = new Map<string, Node>(writings.map((w) => [w.id, w]));
+  return writings
+    .filter((w) => w.nodeType !== 'folder')
+    .map((w) => ({
+      path: `writings/${getNodeZipPath(w, nodeMap)}.md`,
+      content: buildWritingMarkdown(w),
+    }));
+}
+
+/**
+ * Plot のフラットリストから ZipEntry[] を生成する。
+ */
+export function buildPlotEntries(plots: Plot[]): ZipEntry[] {
+  const nodeMap = new Map<string, Node>(plots.map((p) => [p.id, p]));
+  return plots
+    .filter((p) => p.nodeType !== 'folder')
+    .map((p) => ({
+      path: `plots/${getNodeZipPath(p, nodeMap)}.md`,
+      content: buildPlotMarkdown(p),
+    }));
+}
+
+/**
+ * Character のフラットリストから ZipEntry[] を生成する。
+ */
+export function buildCharacterEntries(characters: Character[]): ZipEntry[] {
+  const nodeMap = new Map<string, Node>(characters.map((c) => [c.id, c]));
+  return characters
+    .filter((c) => c.nodeType !== 'folder')
+    .map((c) => ({
+      path: `characters/${getNodeZipPath(c, nodeMap)}.md`,
+      content: buildCharacterMarkdown(c),
+    }));
+}
+
+/**
+ * Memo のフラットリストから ZipEntry[] を生成する。
+ */
+export function buildMemoEntries(memos: Memo[]): ZipEntry[] {
+  const nodeMap = new Map<string, Node>(memos.map((m) => [m.id, m]));
+  return memos
+    .filter((m) => m.nodeType !== 'folder')
+    .map((m) => ({
+      path: `memos/${getNodeZipPath(m, nodeMap)}.md`,
+      content: buildMemoMarkdown(m),
+    }));
+}
diff --git a/packages/adapter/local/src/internal/utils/fs.ts b/packages/adapter/local/src/internal/utils/fs.ts
index 3a0a3c3..dca4387 100644
--- a/packages/adapter/local/src/internal/utils/fs.ts
+++ b/packages/adapter/local/src/internal/utils/fs.ts
@@ -1,6 +1,7 @@
 import {
   readTextFile,
   writeTextFile,
+  writeFile,
   exists,
   mkdir,
   readDir,
@@ -47,6 +48,13 @@ export async function listDir(path: string): Promise<string[]> {
   return entries.map((e) => e.name);
 }
 
+export async function writeBinaryFile(
+  path: string,
+  data: Uint8Array,
+): Promise<void> {
+  await writeFile(path, data);
+}
+
 export async function listSubDirs(path: string): Promise<string[]> {
   if (!(await exists(path))) {
     return [];
diff --git a/packages/ui/src/components/features/editor/project-editor.tsx b/packages/ui/src/components/features/editor/project-editor.tsx
index 9922a29..ae06b08 100644
--- a/packages/ui/src/components/features/editor/project-editor.tsx
+++ b/packages/ui/src/components/features/editor/project-editor.tsx
@@ -2,6 +2,8 @@ import * as React from 'react';
 import { ScrollArea } from '@/components/ui/scroll-area';
 import { Textarea } from '@/components/ui/textarea';
 import { Input } from '@/components/ui/input';
+import { Button } from '@/components/ui/button';
+import { DownloadIcon, LoaderCircleIcon } from 'lucide-react';
 import { cn } from '@/lib/utils';
 
 export interface ProjectEditorData {
@@ -16,6 +18,8 @@ export interface ProjectEditorData {
 export interface ProjectEditorProps {
   data: ProjectEditorData;
   onChange?: (field: keyof ProjectEditorData, value: string) => void;
+  onExport?: () => void;
+  isExporting?: boolean;
   className?: string;
   readOnly?: boolean;
 }
@@ -48,6 +52,8 @@ const textareaFields: {
 export function ProjectEditor({
   data,
   onChange,
+  onExport,
+  isExporting = false,
   className,
   readOnly = false,
 }: ProjectEditorProps) {
@@ -107,6 +113,23 @@ export function ProjectEditor({
           </div>
         </div>
       </ScrollArea>
+      {onExport && (
+        <div className="border-t px-6 py-4">
+          <Button
+            variant="outline"
+            size="sm"
+            onClick={onExport}
+            disabled={isExporting}
+          >
+            {isExporting ? (
+              <LoaderCircleIcon className="mr-2 size-4 animate-spin" />
+            ) : (
+              <DownloadIcon className="mr-2 size-4" />
+            )}
+            {isExporting ? 'エクスポート中...' : 'エクスポート (zip)'}
+          </Button>
+        </div>
+      )}
     </div>
   );
 }
diff --git a/packages/ui/src/components/features/project-list/project-list.stories.tsx b/packages/ui/src/components/features/project-list/project-list.stories.tsx
index 90a71f4..ee3f7e4 100644
--- a/packages/ui/src/components/features/project-list/project-list.stories.tsx
+++ b/packages/ui/src/components/features/project-list/project-list.stories.tsx
@@ -87,17 +87,28 @@ export const Loading: Story = {
 export const Interactive: StoryObj = {
   render: () => {
     const [selectedId, setSelectedId] = useState<string | null>(null);
+    const [exportingProjectId, setExportingProjectId] = useState<string | null>(
+      null,
+    );
 
     const handleSelect = (project: ProjectItem) => {
       setSelectedId(project.id);
       console.log('Selected project:', project);
     };
 
+    const handleExport = (project: ProjectItem) => {
+      setExportingProjectId(project.id);
+      console.log('Exporting project:', project);
+      setTimeout(() => setExportingProjectId(null), 2000);
+    };
+
     return (
       <ProjectList
         projects={mockProjects}
         selectedId={selectedId}
+        exportingProjectId={exportingProjectId}
         onSelect={handleSelect}
+        onExport={handleExport}
       />
     );
   },
diff --git a/packages/ui/src/components/features/project-list/project-list.tsx b/packages/ui/src/components/features/project-list/project-list.tsx
index 785dc3a..8fd9017 100644
--- a/packages/ui/src/components/features/project-list/project-list.tsx
+++ b/packages/ui/src/components/features/project-list/project-list.tsx
@@ -8,6 +8,8 @@ import {
   CommandItem,
 } from '@/components/ui/command';
 import { Skeleton } from '@/components/ui/skeleton';
+import { Button } from '@/components/ui/button';
+import { DownloadIcon, LoaderCircleIcon } from 'lucide-react';
 import { cn } from '@/lib/utils';
 
 export interface ProjectItem {
@@ -21,6 +23,8 @@ export interface ProjectListProps {
   isLoading?: boolean;
   selectedId?: string | null;
   onSelect?: (project: ProjectItem) => void;
+  onExport?: (project: ProjectItem) => void;
+  exportingProjectId?: string | null;
   placeholder?: string;
   emptyMessage?: string;
   className?: string;
@@ -70,6 +74,8 @@ export function ProjectList({
   isLoading = false,
   selectedId,
   onSelect,
+  onExport,
+  exportingProjectId,
   placeholder = 'プロジェクトの検索',
   emptyMessage = 'プロジェクトが見つかりません',
   className,
@@ -110,7 +116,7 @@ export function ProjectList({
                     >
                       {getInitial(project.name)}
                     </div>
-                    <div className="flex min-w-0 flex-col">
+                    <div className="flex min-w-0 flex-1 flex-col">
                       <span className="truncate text-sm font-medium">
                         {project.name}
                       </span>
@@ -120,6 +126,24 @@ export function ProjectList({
                         </span>
                       )}
                     </div>
+                    {onExport && (
+                      <Button
+                        variant="ghost"
+                        size="icon-sm"
+                        disabled={exportingProjectId != null}
+                        onClick={(e) => {
+                          e.stopPropagation();
+                          onExport(project);
+                        }}
+                        onPointerDown={(e) => e.stopPropagation()}
+                      >
+                        {exportingProjectId === project.id ? (
+                          <LoaderCircleIcon className="size-4 animate-spin" />
+                        ) : (
+                          <DownloadIcon className="size-4" />
+                        )}
+                      </Button>
+                    )}
                   </CommandItem>
                 ))}
               </CommandGroup>