diff --git a/sdks/sandbox/python/src/opensandbox/adapters/converter/sandbox_model_converter.py b/sdks/sandbox/python/src/opensandbox/adapters/converter/sandbox_model_converter.py
index a25ddd698..e0129fcb4 100644
--- a/sdks/sandbox/python/src/opensandbox/adapters/converter/sandbox_model_converter.py
+++ b/sdks/sandbox/python/src/opensandbox/adapters/converter/sandbox_model_converter.py
@@ -128,11 +128,11 @@ def to_api_volume(volume: Volume):
         from opensandbox.api.lifecycle.types import UNSET
 
         api_host = UNSET
-        if volume.host is not None:
+        if volume.host is not None and not isinstance(volume.host, Unset):
             api_host = ApiHost(path=volume.host.path)
 
         api_pvc = UNSET
-        if volume.pvc is not None:
+        if volume.pvc is not None and not isinstance(volume.pvc, Unset):
             api_pvc = ApiPVC(
                 claim_name=volume.pvc.claim_name,
                 create_if_not_exists=volume.pvc.create_if_not_exists,
@@ -143,7 +143,12 @@ def to_api_volume(volume: Volume):
             )
 
         api_ossfs = UNSET
-        if volume.ossfs is not None and volume.ossfs.access_key_id is not None and volume.ossfs.access_key_secret is not None:
+        if (
+            volume.ossfs is not None
+            and not isinstance(volume.ossfs, Unset)
+            and volume.ossfs.access_key_id is not None
+            and volume.ossfs.access_key_secret is not None
+        ):
             api_ossfs = ApiOSSFS(
                 bucket=volume.ossfs.bucket,
                 endpoint=volume.ossfs.endpoint,
@@ -154,7 +159,7 @@ def to_api_volume(volume: Volume):
             )
 
         api_sub_path = UNSET
-        if volume.sub_path is not None:
+        if volume.sub_path is not None and not isinstance(volume.sub_path, Unset):
             api_sub_path = volume.sub_path
 
         return ApiVolume(
diff --git a/sdks/sandbox/python/tests/test_converters_and_error_handling.py b/sdks/sandbox/python/tests/test_converters_and_error_handling.py
index cab7a4c33..6912ad1a1 100644
--- a/sdks/sandbox/python/tests/test_converters_and_error_handling.py
+++ b/sdks/sandbox/python/tests/test_converters_and_error_handling.py
@@ -684,6 +684,66 @@ def test_sandbox_model_converter_snapshot_restore_request() -> None:
     assert "image" not in dumped
     assert "entrypoint" not in dumped
 
+def test_sandbox_model_converter_to_api_volume_skips_unset_fields() -> None:
+    from opensandbox.api.lifecycle.types import UNSET
+    from opensandbox.models.sandboxes import Volume
+
+    # Inject UNSET into backend fields (bypassing Pydantic validation) to
+    # simulate a domain Volume carrying Unset values from an API round-trip.
+    volume = Volume.model_construct(
+        name="workdir",
+        mount_path="/mnt/work",
+        read_only=False,
+        host=UNSET,
+        pvc=UNSET,
+        ossfs=UNSET,
+        sub_path=UNSET,
+    )
+
+    api_volume = SandboxModelConverter.to_api_volume(volume)
+    dumped = api_volume.to_dict()
+    assert dumped == {"name": "workdir", "mountPath": "/mnt/work", "readOnly": False}
+    assert "host" not in dumped
+    assert "pvc" not in dumped
+    assert "ossfs" not in dumped
+    assert "subPath" not in dumped
+
+def test_sandbox_model_converter_to_api_volume_maps_backends() -> None:
+    from opensandbox.models.sandboxes import OSSFS, PVC, Host, Volume
+
+    volume = Volume(
+        name="workdir",
+        host=Host(path="/data/opensandbox"),
+        mount_path="/mnt/work",
+        sub_path="sub",
+    )
+    dumped = SandboxModelConverter.to_api_volume(volume).to_dict()
+    assert dumped["host"] == {"path": "/data/opensandbox"}
+    assert dumped["subPath"] == "sub"
+    assert "pvc" not in dumped
+    assert "ossfs" not in dumped
+
+    pvc_volume = Volume(
+        name="models",
+        pvc=PVC(claim_name="shared-models-pvc"),
+        mount_path="/mnt/models",
+        read_only=True,
+    )
+    pvc_dumped = SandboxModelConverter.to_api_volume(pvc_volume).to_dict()
+    assert pvc_dumped["pvc"]["claimName"] == "shared-models-pvc"
+    assert pvc_dumped["readOnly"] is True
+
+    ossfs_volume = Volume(
+        name="oss", ossfs=OSSFS(
+            bucket="b",
+            endpoint="oss-cn-hangzhou.aliyuncs.com",
+            accessKeyId="ak",
+            accessKeySecret="sk",
+        ),
+        mount_path="/mnt/oss",
+    )
+    ossfs_dumped = SandboxModelConverter.to_api_volume(ossfs_volume).to_dict()
+    assert ossfs_dumped["ossfs"]["bucket"] == "b"
 
 def test_sandbox_model_converter_maps_platform_from_create_response() -> None:
     from opensandbox.api.lifecycle.models.create_sandbox_response import (