diff --git a/graphene/types/typemap.py b/graphene/types/typemap.py
index dce04445..9edb8518 100644
--- a/graphene/types/typemap.py
+++ b/graphene/types/typemap.py
@@ -255,6 +255,7 @@ class TypeMap(GraphQLTypeMap):
         return GrapheneUnionType(
             graphene_type=type,
             name=type._meta.name,
+            description=type._meta.description,
             types=types,
             resolve_type=_resolve_type,
         )