diff --git a/libs/vertexai/langchain_google_vertexai/chat_models.py b/libs/vertexai/langchain_google_vertexai/chat_models.py
index 5dc5bca3a..07ac9c7d0 100644
--- a/libs/vertexai/langchain_google_vertexai/chat_models.py
+++ b/libs/vertexai/langchain_google_vertexai/chat_models.py
@@ -443,7 +443,7 @@ def _convert_to_parts(message: BaseMessage) -> List[Part]:
             vertex_messages.append(Content(role=role, parts=parts))
         elif isinstance(message, FunctionMessage):
             prev_ai_message = None
-            role = "function"
+            role = "user"
 
             part = Part(
                 function_response=FunctionResponse(
@@ -453,9 +453,7 @@ def _convert_to_parts(message: BaseMessage) -> List[Part]:
             parts = [part]
             if vertex_messages:
                 prev_content = vertex_messages[-1]
-                prev_content_is_function = (
-                    prev_content and prev_content.role == "function"
-                )
+                prev_content_is_function = prev_content and prev_content.role == "user"
                 if prev_content_is_function:
                     prev_parts = list(prev_content.parts)
                     prev_parts.extend(parts)
@@ -465,7 +463,7 @@ def _convert_to_parts(message: BaseMessage) -> List[Part]:
 
             vertex_messages.append(Content(role=role, parts=parts))
         elif isinstance(message, ToolMessage):
-            role = "function"
+            role = "user"
 
             # message.name can be null for ToolMessage
             name = message.name
@@ -527,9 +525,9 @@ def _parse_content(raw_content: str | Dict[Any, Any]) -> Dict[Any, Any]:
             parts = [part]
 
             prev_content = vertex_messages[-1]
-            prev_content_is_function = prev_content and prev_content.role == "function"
+            prev_content_is_tool_response = prev_content and prev_content.role == "user"
 
-            if prev_content_is_function:
+            if prev_content_is_tool_response:
                 prev_parts = list(prev_content.parts)
                 prev_parts.extend(parts)
                 # replacing last message
diff --git a/libs/vertexai/tests/unit_tests/test_chat_models.py b/libs/vertexai/tests/unit_tests/test_chat_models.py
index d6d92ec02..8487efe42 100644
--- a/libs/vertexai/tests/unit_tests/test_chat_models.py
+++ b/libs/vertexai/tests/unit_tests/test_chat_models.py
@@ -333,7 +333,7 @@ def test_parse_history_gemini_function_empty_list() -> None:
         name=tool_call_1["name"], args=tool_call_1["args"]
     )
 
-    assert history[2].role == "function"
+    assert history[2].role == "user"
     assert history[2].parts[0].function_response == FunctionResponse(
         name=fn_name_1,
         response={"content": ""},
@@ -414,7 +414,7 @@ def test_parse_history_gemini_function() -> None:
         name=tool_call_2["name"], args=tool_call_2["args"]
     )
 
-    assert history[2].role == "function"
+    assert history[2].role == "user"
     assert history[2].parts[0].function_response == FunctionResponse(
         name=fn_name_1,
         response={"content": message3.content},
@@ -429,7 +429,7 @@ def test_parse_history_gemini_function() -> None:
         name=tool_call_3["name"], args=tool_call_3["args"]
     )
 
-    assert history[4].role == "function"
+    assert history[4].role == "user"
     assert history[4].parts[0].function_response == FunctionResponse(
         name=fn_name_3,
         response={"content": message6.content},
@@ -1246,7 +1246,7 @@ def test_multiple_fc() -> None:
                     )
                 ),
             ],
-            role="function",
+            role="user",
         ),
     ]
     assert history == expected
@@ -1549,7 +1549,7 @@ def test_thought_signature() -> None:
             ],
         ),
         Content(
-            role="function",
+            role="user",
             parts=[
                 Part(
                     function_response=FunctionResponse(