diff --git a/src/google/adk/tools/_function_parameter_parse_util.py b/src/google/adk/tools/_function_parameter_parse_util.py
index a0168fbe2..6d5cfc687 100644
--- a/src/google/adk/tools/_function_parameter_parse_util.py
+++ b/src/google/adk/tools/_function_parameter_parse_util.py
@@ -27,6 +27,7 @@
 
 from google.genai import types
 import pydantic
+from enum import Enum
 
 from ..utils.variant_utils import GoogleLLMVariant
 
@@ -75,7 +76,7 @@ def _raise_if_schema_unsupported(
 ):
   if variant == GoogleLLMVariant.GEMINI_API:
     _raise_for_any_of_if_mldev(schema)
-    _update_for_default_if_mldev(schema)
+    # _update_for_default_if_mldev(schema) # No need of this since GEMINI now supports default value
 
 
 def _is_default_value_compatible(
@@ -145,6 +146,16 @@ def _parse_schema_from_parameter(
     schema.type = _py_builtin_type_to_schema_type[param.annotation]
     _raise_if_schema_unsupported(variant, schema)
     return schema
+  if isinstance(param.annotation, type) and issubclass(param.annotation, Enum):
+      schema.type = types.Type.STRING
+      schema.enum = [e.value for e in param.annotation]
+      if param.default is not inspect.Parameter.empty:
+          default_value = param.default.value if isinstance(param.default, Enum) else param.default
+          if default_value not in schema.enum:
+              raise ValueError(default_value_error_msg)
+          schema.default = default_value
+      _raise_if_schema_unsupported(variant, schema)
+      return schema
   if (
       get_origin(param.annotation) is Union
       # only parse simple UnionType, example int | str | float | bool
diff --git a/tests/unittests/tools/test_build_function_declaration.py b/tests/unittests/tools/test_build_function_declaration.py
index edf3c7128..33d72c051 100644
--- a/tests/unittests/tools/test_build_function_declaration.py
+++ b/tests/unittests/tools/test_build_function_declaration.py
@@ -22,7 +22,8 @@
 # TODO: crewai requires python 3.10 as minimum
 # from crewai_tools import FileReadTool
 from pydantic import BaseModel
-
+from enum import Enum
+import pytest
 
 def test_string_input():
   def simple_function(input_str: str) -> str:
@@ -219,6 +220,32 @@ def simple_function(
   assert function_decl.parameters.properties['input_dir'].type == 'ARRAY'
   assert function_decl.parameters.properties['input_dir'].items.type == 'OBJECT'
 
+def test_enums():
+
+  class InputEnum(Enum):
+    AGENT = "agent"
+    TOOL = "tool"
+
+  def simple_function(input:InputEnum=InputEnum.AGENT):
+    return input.value
+
+  function_decl = _automatic_function_calling_util.build_function_declaration(
+    func=simple_function
+  )
+
+  assert function_decl.name == 'simple_function'
+  assert function_decl.parameters.type == 'OBJECT'
+  assert function_decl.parameters.properties['input'].type == 'STRING'
+  assert function_decl.parameters.properties['input'].default == 'agent'
+  assert function_decl.parameters.properties['input'].enum == ['agent', 'tool']
+
+  def simple_function_with_wrong_enum(input:InputEnum="WRONG_ENUM"):
+    return input.value
+
+  with pytest.raises(ValueError):
+    _automatic_function_calling_util.build_function_declaration(
+      func=simple_function_with_wrong_enum
+    )
 
 def test_basemodel_list():
   class ChildInput(BaseModel):