diff --git a/moto/kms/responses.py b/moto/kms/responses.py
index dc37c8b59..fe7d28523 100644
--- a/moto/kms/responses.py
+++ b/moto/kms/responses.py
@@ -9,6 +9,7 @@ from boto.exception import JSONResponseError
 from boto.kms.exceptions import AlreadyExistsException, NotFoundException
 
 from moto.core.responses import BaseResponse
+from moto.core.utils import iso_8601_datetime_without_milliseconds
 from .models import kms_backends
 
 reserved_aliases = [
@@ -272,7 +273,7 @@ class KmsResponse(BaseResponse):
         try:
             return json.dumps({
                 'KeyId': key_id,
-                'DeletionDate': self.kms_backend.schedule_key_deletion(key_id)
+                'DeletionDate': iso_8601_datetime_without_milliseconds(self.kms_backend.schedule_key_deletion(key_id))
             })
         except KeyError:
             raise JSONResponseError(404, 'Not Found', body={