diff --git a/src/google/adk/tools/openapi_tool/auth/auth_helpers.py b/src/google/adk/tools/openapi_tool/auth/auth_helpers.py
index e8eba69a94..cc8464d997 100644
--- a/src/google/adk/tools/openapi_tool/auth/auth_helpers.py
+++ b/src/google/adk/tools/openapi_tool/auth/auth_helpers.py
@@ -14,6 +14,8 @@
 
 from __future__ import annotations
 
+import base64
+
 from typing import Any
 from typing import Dict
 from typing import List
@@ -387,16 +389,25 @@ def credential_to_param(
       }
       return param, kwargs
     elif (
-        auth_credential
-        and auth_credential.http
+        auth_credential.http
+        and auth_credential.http.scheme.lower() == "basic"
         and auth_credential.http.credentials
-        and (
-            auth_credential.http.credentials.username
-            or auth_credential.http.credentials.password
-        )
+        and auth_credential.http.credentials.username is not None
+        and auth_credential.http.credentials.password is not None
     ):
-      # Basic Auth is explicitly NOT supported
-      raise NotImplementedError("Basic Authentication is not supported.")
+      credentials = auth_credential.http.credentials
+      encoded_credentials = base64.b64encode(
+          f"{credentials.username}:{credentials.password}".encode("utf-8")
+      ).decode("ascii")
+      param = ApiParameter(
+          original_name="Authorization",
+          param_location="header",
+          param_schema=Schema(type="string"),
+          description=auth_scheme.description or "Basic authentication",
+          py_name=INTERNAL_AUTH_PREFIX + "Authorization",
+      )
+      kwargs = {param.py_name: f"Basic {encoded_credentials}"}
+      return param, kwargs
     else:
       raise ValueError("Invalid HTTP auth credentials")
 
diff --git a/tests/unittests/tools/openapi_tool/auth/test_auth_helper.py b/tests/unittests/tools/openapi_tool/auth/test_auth_helper.py
index 3f5e8f07b5..fe9be5a7ab 100644
--- a/tests/unittests/tools/openapi_tool/auth/test_auth_helper.py
+++ b/tests/unittests/tools/openapi_tool/auth/test_auth_helper.py
@@ -12,6 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import base64
 from unittest.mock import patch
 
 from fastapi.openapi.models import APIKey
@@ -411,7 +412,7 @@ def test_credential_to_param_http_bearer():
   assert kwargs == {INTERNAL_AUTH_PREFIX + "Authorization": "Bearer test_token"}
 
 
-def test_credential_to_param_http_basic_not_supported():
+def test_credential_to_param_http_basic():
   auth_scheme = HTTPBase(scheme="basic")
   auth_credential = AuthCredential(
       auth_type=AuthCredentialTypes.HTTP,
@@ -421,9 +422,27 @@ def test_credential_to_param_http_basic_not_supported():
       ),
   )
 
-  with pytest.raises(
-      NotImplementedError, match="Basic Authentication is not supported."
-  ):
+  param, kwargs = credential_to_param(auth_scheme, auth_credential)
+
+  expected_credentials = base64.b64encode(b"user:password").decode("ascii")
+  assert param.original_name == "Authorization"
+  assert param.param_location == "header"
+  assert kwargs == {
+      INTERNAL_AUTH_PREFIX + "Authorization": f"Basic {expected_credentials}"
+  }
+
+
+def test_credential_to_param_http_basic_missing_password():
+  auth_scheme = HTTPBase(scheme="basic")
+  auth_credential = AuthCredential(
+      auth_type=AuthCredentialTypes.HTTP,
+      http=HttpAuth(
+          scheme="basic",
+          credentials=HttpCredentials(username="user"),
+      ),
+  )
+
+  with pytest.raises(ValueError, match="Invalid HTTP auth credentials"):
     credential_to_param(auth_scheme, auth_credential)