diff --git a/ryu/lib/stringify.py b/ryu/lib/stringify.py
index ca762416..8a865b7e 100644
--- a/ryu/lib/stringify.py
+++ b/ryu/lib/stringify.py
@@ -188,7 +188,11 @@ class StringifyMixin(object):
     def _get_default_encoder(cls, encode_string):
         def _encode(v):
             if isinstance(v, (bytes, six.text_type)):
+                if isinstance(v, six.text_type):
+                    v = v.encode('utf-8')
                 json_value = encode_string(v)
+                if six.PY3:
+                    json_value = json_value.decode('ascii')
             elif isinstance(v, list):
                 json_value = list(map(_encode, v))
             elif isinstance(v, dict):
diff --git a/ryu/lib/type_desc.py b/ryu/lib/type_desc.py
index 612be379..d96fc51f 100644
--- a/ryu/lib/type_desc.py
+++ b/ryu/lib/type_desc.py
@@ -112,5 +112,11 @@ class IPv6Addr(TypeDescr):
 class UnknownType(TypeDescr):
     import base64
 
-    to_user = staticmethod(base64.b64encode)
+    b64encode = base64.b64encode
+    if six.PY3:
+        @classmethod
+        def to_user(cls, data):
+            return cls.b64encode(data).decode('ascii')
+    else:
+        to_user = staticmethod(base64.b64encode)
     from_user = staticmethod(base64.b64decode)