diff --git a/src/google/adk/tools/_function_parameter_parse_util.py b/src/google/adk/tools/_function_parameter_parse_util.py
index 1b9559b29c..3c848ef281 100644
--- a/src/google/adk/tools/_function_parameter_parse_util.py
+++ b/src/google/adk/tools/_function_parameter_parse_util.py
@@ -247,7 +247,7 @@ def _parse_schema_from_parameter(
     _raise_if_schema_unsupported(variant, schema)
     return schema
   if (
-      get_origin(param.annotation) is Union
+      get_origin(param.annotation) in (Union, typing_types.UnionType)
       # only parse simple UnionType, example int | str | float | bool
       # complex types.UnionType will be invoked in raise branch
       and all(
@@ -330,7 +330,7 @@ def _parse_schema_from_parameter(
         schema.default = param.default
       _raise_if_schema_unsupported(variant, schema)
       return schema
-    if origin is Union:
+    if origin in (Union, typing_types.UnionType):
       schema.any_of = []
       schema.type = types.Type.OBJECT
       unique_types = set()
diff --git a/src/google/adk/tools/base_tool.py b/src/google/adk/tools/base_tool.py
index 8dd112a6c8..da6423ae0d 100644
--- a/src/google/adk/tools/base_tool.py
+++ b/src/google/adk/tools/base_tool.py
@@ -17,6 +17,7 @@
 from abc import ABC
 import inspect
 import logging
+import types as typing_types
 from typing import Any
 from typing import Callable
 from typing import get_args
@@ -168,7 +169,7 @@ def from_config(
         value = config_dict[param_name]
 
         # Get the actual type T of the parameter if it's Optional[T]
-        if get_origin(param_type) is Union:
+        if get_origin(param_type) in (Union, typing_types.UnionType):
           # This is Optional[T] which is Union[T, None]
           args = get_args(param_type)
           if len(args) == 2 and type(None) in args:
diff --git a/src/google/adk/tools/function_tool.py b/src/google/adk/tools/function_tool.py
index de59755365..caf2491e2f 100644
--- a/src/google/adk/tools/function_tool.py
+++ b/src/google/adk/tools/function_tool.py
@@ -16,6 +16,7 @@
 
 import inspect
 import logging
+import types as typing_types
 from typing import Any
 from typing import Callable
 from typing import get_args
@@ -122,7 +123,7 @@ def _preprocess_args(self, args: dict[str, Any]) -> dict[str, Any]:
         target_type = param.annotation
 
         # Handle Optional[PydanticModel] types
-        if get_origin(param.annotation) is Union:
+        if get_origin(param.annotation) in (Union, typing_types.UnionType):
           union_args = get_args(param.annotation)
           # Find the non-None type in Optional[T] (which is Union[T, None])
           non_none_types = [arg for arg in union_args if arg is not type(None)]