diff --git a/mistral/engine/action_handler.py b/mistral/engine/action_handler.py
index c673ca56..6e3fefeb 100644
--- a/mistral/engine/action_handler.py
+++ b/mistral/engine/action_handler.py
@@ -93,7 +93,11 @@ def get_action_input(action_name, input_dict, wf_name=None, wf_spec=None):
 
     if action_def.action_class:
         _inject_action_ctx_for_validating(action_def, input_dict)
-    e_utils.validate_input(action_def, input_dict)
+
+    # NOTE(xylan): Don't validate action input if action initialization method
+    # contains ** argument.
+    if '**' not in action_def.input:
+        e_utils.validate_input(action_def, input_dict)
 
     if action_def.spec:
         # Ad-hoc action.
diff --git a/mistral/tests/unit/actions/test_action_manager.py b/mistral/tests/unit/actions/test_action_manager.py
index a92b1523..520f7302 100644
--- a/mistral/tests/unit/actions/test_action_manager.py
+++ b/mistral/tests/unit/actions/test_action_manager.py
@@ -38,6 +38,12 @@ class ActionManagerTest(base.DbTestCase):
         self._assert_single_item(action_list, name="nova.servers_get")
         self._assert_single_item(action_list, name="nova.volumes_delete")
 
+        server_find_action = self._assert_single_item(
+            action_list,
+            name="nova.servers_find"
+        )
+        self.assertIn('**', server_find_action.input)
+
         self._assert_single_item(action_list, name="keystone.users_list")
         self._assert_single_item(action_list, name="keystone.trusts_create")
 
diff --git a/mistral/tests/unit/engine/test_run_action.py b/mistral/tests/unit/engine/test_run_action.py
index 1b3e0e09..b40f1190 100644
--- a/mistral/tests/unit/engine/test_run_action.py
+++ b/mistral/tests/unit/engine/test_run_action.py
@@ -12,9 +12,11 @@
 #    See the License for the specific language governing permissions and
 #    limitations under the License.
 
+import mock
 from oslo_config import cfg
 
 from mistral.db.v2 import api as db_api
+from mistral.db.v2.sqlalchemy import models
 from mistral import exceptions as exc
 from mistral.services import actions
 from mistral.tests.unit.engine import base
@@ -103,3 +105,40 @@ class RunActionEngineTest(base.EngineTestCase):
         )
 
         self.assertIn('concat', exception.message)
+
+    @mock.patch('mistral.engine.action_handler.resolve_action_definition')
+    @mock.patch('mistral.engine.utils.validate_input')
+    @mock.patch('mistral.services.action_manager.get_action_class')
+    @mock.patch('mistral.engine.action_handler.run_action')
+    def test_run_action_with_kwargs_input(self, run_mock, class_mock,
+                                          validate_mock, def_mock):
+        action_def = models.ActionDefinition()
+        action_def.update({
+            'name': 'fake_action',
+            'action_class': '',
+            'attributes': {},
+            'description': '',
+            'input': '**kwargs',
+            'is_system': True,
+            'scope': 'public'
+        })
+        def_mock.return_value = action_def
+
+        class_ret = mock.MagicMock()
+        class_mock.return_value = class_ret
+
+        self.engine.start_action('fake_action', {'input': 'Hello'})
+
+        self.assertEqual(2, def_mock.call_count)
+        def_mock.assert_called_with('fake_action', None, None)
+
+        self.assertEqual(0, validate_mock.call_count)
+
+        class_ret.assert_called_once_with(input='Hello')
+
+        run_mock.assert_called_once_with(
+            action_def,
+            {'input': 'Hello'},
+            target=None,
+            async=False
+        )
diff --git a/mistral/utils/inspect_utils.py b/mistral/utils/inspect_utils.py
index 2cbc099d..3e31ae69 100644
--- a/mistral/utils/inspect_utils.py
+++ b/mistral/utils/inspect_utils.py
@@ -71,4 +71,7 @@ def get_arg_list_as_str(func):
         else:
             arg_str_list.append("%s" % args[index])
 
+    if argspec.keywords:
+        arg_str_list.append("**%s" % argspec.keywords)
+
     return ", ".join(arg_str_list)