diff --git a/src/google/adk/tools/_function_parameter_parse_util.py b/src/google/adk/tools/_function_parameter_parse_util.py
index a0168fbe219..9e91bb59caf 100644
--- a/src/google/adk/tools/_function_parameter_parse_util.py
+++ b/src/google/adk/tools/_function_parameter_parse_util.py
@@ -15,6 +15,7 @@
 
 from __future__ import annotations
 
+from enum import Enum
 import inspect
 import logging
 import types as typing_types
@@ -145,6 +146,17 @@ 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:
+      if not _is_default_value_compatible(param.default, param.annotation):
+        raise ValueError(default_value_error_msg)
+      schema.default = param.default
+    _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 edf3c7128eb..67e80dd21ae 100644
--- a/tests/unittests/tools/test_build_function_declaration.py
+++ b/tests/unittests/tools/test_build_function_declaration.py
@@ -102,6 +102,26 @@ def simple_function(input_str: Dict[str, str]) -> str:
   assert function_decl.parameters.properties['input_str'].type == 'OBJECT'
 
 
+def test_enum_input():
+  from enum import Enum
+
+  class Color(str, Enum):
+    RED = 'red'
+    GREEN = 'green'
+    BLUE = 'blue'
+
+  def simple_function(input_str: Color) -> str:
+    return {'result': input_str}
+
+  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_str'].type == 'STRING'
+
+
 def test_basemodel_input():
   class CustomInput(BaseModel):
     input_str: str