diff --git a/heat/engine/clients/os/keystone/heat_keystoneclient.py b/heat/engine/clients/os/keystone/heat_keystoneclient.py
index 110b2fa0d5..21131d30b7 100644
--- a/heat/engine/clients/os/keystone/heat_keystoneclient.py
+++ b/heat/engine/clients/os/keystone/heat_keystoneclient.py
@@ -238,11 +238,11 @@ class KsClientWrapper(object):
             pass
 
     def _get_username(self, username):
-        if(len(username) > 64):
-            LOG.warning("Truncating the username %s to the last 64 "
+        if(len(username) > 255):
+            LOG.warning("Truncating the username %s to the last 255 "
                         "characters.", username)
-        # get the last 64 characters of the username
-        return username[-64:]
+        # get the last 255 characters of the username
+        return username[-255:]
 
     def create_stack_user(self, username, password=''):
         """Create a user defined as part of a stack.
diff --git a/heat/tests/clients/test_heat_client.py b/heat/tests/clients/test_heat_client.py
index ae3ffbce9e..e17427ceb3 100644
--- a/heat/tests/clients/test_heat_client.py
+++ b/heat/tests/clients/test_heat_client.py
@@ -153,22 +153,22 @@ class KeystoneClientTest(common.HeatTestCase):
         return mock_ks_auth, mock_auth_ref
 
     def test_username_length(self):
-        """Test that user names >64 characters are properly truncated."""
+        """Test that user names >255 characters are properly truncated."""
 
         self._stubs_auth()
 
         ctx = utils.dummy_context()
         ctx.trust_id = None
 
-        # a >64 character user name and the expected version
-        long_user_name = 'U' * 64 + 'S'
-        good_user_name = long_user_name[-64:]
+        # a >255 character user name and the expected version
+        long_user_name = 'U' * 255 + 'S'
+        good_user_name = 'U' * 254 + 'S'
         # mock keystone client user functions
         self.mock_ks_v3_client.users = self.m.CreateMockAnything()
         mock_user = self.m.CreateMockAnything()
         mock_user.id = 'auser123'
         # when keystone is called, the name should have been truncated
-        # to the last 64 characters of the long name
+        # to the last 255 characters of the long name
         self.mock_ks_v3_client.users.create(name=good_user_name,
                                             password='password',
                                             default_project=ctx.tenant_id
diff --git a/heat_integrationtests/common/test.py b/heat_integrationtests/common/test.py
index f2e7dd75c2..842f4e774b 100644
--- a/heat_integrationtests/common/test.py
+++ b/heat_integrationtests/common/test.py
@@ -61,7 +61,7 @@ def call_until_true(duration, sleep_for, func, *args, **kwargs):
 
 
 def rand_name(name=''):
-    randbits = str(random.randint(1, 0x7fffffff))
+    randbits = six.text_type(random.randint(1, 0x7fffffff))
     if name:
         return name + '-' + randbits
     else:
diff --git a/releasenotes/notes/change-heat-keystone-user-name-limit-to-255-bd076132b98744be.yaml b/releasenotes/notes/change-heat-keystone-user-name-limit-to-255-bd076132b98744be.yaml
new file mode 100644
index 0000000000..eeaf4fc767
--- /dev/null
+++ b/releasenotes/notes/change-heat-keystone-user-name-limit-to-255-bd076132b98744be.yaml
@@ -0,0 +1,5 @@
+---
+other:
+  - Now heat keystone user name charaters limit increased from 64 to 255.
+    Any extra charaters will lost when truncate the name to the last 255
+    charaters.