diff --git a/src/google/adk/models/anthropic_llm.py b/src/google/adk/models/anthropic_llm.py
index 1f7f37b043..1ca6a3deb5 100644
--- a/src/google/adk/models/anthropic_llm.py
+++ b/src/google/adk/models/anthropic_llm.py
@@ -90,6 +90,14 @@ def _is_image_part(part: types.Part) -> bool:
   )
 
 
+def _is_document_part(part: types.Part) -> bool:
+  return (
+      part.inline_data
+      and part.inline_data.mime_type
+      and part.inline_data.mime_type.startswith("application/pdf")
+  )
+
+
 def part_to_message_block(
     part: types.Part,
 ) -> Union[
@@ -151,6 +159,14 @@ def part_to_message_block(
             type="base64", media_type=part.inline_data.mime_type, data=data
         ),
     )
+  elif _is_document_part(part):
+    data = base64.b64encode(part.inline_data.data).decode()
+    return anthropic_types.DocumentBlockParam(
+        type="document",
+        source=dict(
+            type="base64", media_type=part.inline_data.mime_type, data=data
+        ),
+    )
   elif part.executable_code:
     return anthropic_types.TextBlockParam(
         type="text",
@@ -179,6 +195,13 @@ def content_to_message_param(
       )
       continue
 
+    # Document data is not supported in Claude for assistant turns.
+    if content.role != "user" and _is_document_part(part):
+      logger.warning(
+          "Document data is not supported in Claude for assistant turns."
+      )
+      continue
+
     message_block.append(part_to_message_block(part))
 
   return {
diff --git a/tests/unittests/models/test_anthropic_llm.py b/tests/unittests/models/test_anthropic_llm.py
index 50759659f5..a62982a5fd 100644
--- a/tests/unittests/models/test_anthropic_llm.py
+++ b/tests/unittests/models/test_anthropic_llm.py
@@ -12,6 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import base64
 import json
 import os
 import sys
@@ -526,6 +527,22 @@ def test_part_to_message_block_with_multiple_content_items():
   assert result["content"] == "First part\nSecond part"
 
 
+def test_part_to_message_block_with_pdf_document():
+  """Test that part_to_message_block handles PDF document parts."""
+  pdf_data = b"%PDF-1.4 fake pdf content"
+  part = Part(
+      inline_data=types.Blob(mime_type="application/pdf", data=pdf_data)
+  )
+
+  result = part_to_message_block(part)
+
+  assert isinstance(result, dict)
+  assert result["type"] == "document"
+  assert result["source"]["type"] == "base64"
+  assert result["source"]["media_type"] == "application/pdf"
+  assert result["source"]["data"] == base64.b64encode(pdf_data).decode()
+
+
 content_to_message_param_test_cases = [
     (
         "user_role_with_text_and_image",
@@ -542,7 +559,7 @@ def test_part_to_message_block_with_multiple_content_items():
         ),
         "user",
         2,  # Expected content length
-        False,  # Should not log warning
+        None,  # No warning expected
     ),
     (
         "model_role_with_text_and_image",
@@ -559,7 +576,7 @@ def test_part_to_message_block_with_multiple_content_items():
         ),
         "assistant",
         1,  # Image filtered out, only text remains
-        True,  # Should log warning
+        "Image data is not supported in Claude for assistant turns.",
     ),
     (
         "assistant_role_with_text_and_image",
@@ -576,30 +593,62 @@ def test_part_to_message_block_with_multiple_content_items():
         ),
         "assistant",
         1,  # Image filtered out, only text remains
-        True,  # Should log warning
+        "Image data is not supported in Claude for assistant turns.",
+    ),
+    (
+        "user_role_with_text_and_document",
+        Content(
+            role="user",
+            parts=[
+                Part.from_text(text="Summarize this document."),
+                Part(
+                    inline_data=types.Blob(
+                        mime_type="application/pdf", data=b"fake_pdf_data"
+                    )
+                ),
+            ],
+        ),
+        "user",
+        2,  # Both text and document included
+        None,  # No warning expected
+    ),
+    (
+        "model_role_with_text_and_document",
+        Content(
+            role="model",
+            parts=[
+                Part.from_text(text="Here is the summary."),
+                Part(
+                    inline_data=types.Blob(
+                        mime_type="application/pdf", data=b"fake_pdf_data"
+                    )
+                ),
+            ],
+        ),
+        "assistant",
+        1,  # Document filtered out, only text remains
+        "Document data is not supported in Claude for assistant turns.",
     ),
 ]
 
 
 @pytest.mark.parametrize(
-    "_, content, expected_role, expected_content_length, should_log_warning",
+    "_, content, expected_role, expected_content_length, expected_warning",
     content_to_message_param_test_cases,
     ids=[case[0] for case in content_to_message_param_test_cases],
 )
-def test_content_to_message_param_with_images(
-    _, content, expected_role, expected_content_length, should_log_warning
+def test_content_to_message_param(
+    _, content, expected_role, expected_content_length, expected_warning
 ):
-  """Test content_to_message_param handles images correctly based on role."""
+  """Test content_to_message_param handles images and documents based on role."""
   with mock.patch("google.adk.models.anthropic_llm.logger") as mock_logger:
     result = content_to_message_param(content)
 
     assert result["role"] == expected_role
     assert len(result["content"]) == expected_content_length
 
-    if should_log_warning:
-      mock_logger.warning.assert_called_once_with(
-          "Image data is not supported in Claude for assistant turns."
-      )
+    if expected_warning:
+      mock_logger.warning.assert_called_once_with(expected_warning)
     else:
       mock_logger.warning.assert_not_called()