diff --git a/ryu/app/client.py b/ryu/app/client.py
index 7e8b90fd..e14b3129 100644
--- a/ryu/app/client.py
+++ b/ryu/app/client.py
@@ -18,9 +18,9 @@
 # This module is *not* used by ryu-manager.
 # Imported and used by OpenStack Ryu plug-in and agent.
 
-import httplib
+import http.client
 import json
-import urlparse
+import urllib.parse
 
 
 def ignore_http_not_found(func):
@@ -30,9 +30,9 @@ def ignore_http_not_found(func):
     """
     try:
         func()
-    except httplib.HTTPException as e:
+    except http.client.HTTPException as e:
         res = e.args[0]
-        if res.status != httplib.NOT_FOUND:
+        if res.status != http.client.NOT_FOUND:
             raise
 
 
@@ -40,13 +40,13 @@ class RyuClientBase(object):
     def __init__(self, version, address):
         super(RyuClientBase, self).__init__()
         self.version = version
-        res = urlparse.SplitResult('', address, '', '', '')
+        res = urllib.parse.SplitResult('', address, '', '', '')
         self.host = res.hostname
         self.port = res.port
         self.url_prefix = '/' + self.version + '/'
 
     def _do_request(self, method, action, body=None):
-        conn = httplib.HTTPConnection(self.host, self.port)
+        conn = http.client.HTTPConnection(self.host, self.port)
         url = self.url_prefix + action
         headers = {}
         if body is not None:
@@ -54,13 +54,13 @@ class RyuClientBase(object):
             headers['Content-Type'] = 'application/json'
         conn.request(method, url, body, headers)
         res = conn.getresponse()
-        if res.status in (httplib.OK,
-                          httplib.CREATED,
-                          httplib.ACCEPTED,
-                          httplib.NO_CONTENT):
+        if res.status in (http.client.OK,
+                          http.client.CREATED,
+                          http.client.ACCEPTED,
+                          http.client.NO_CONTENT):
             return res
 
-        raise httplib.HTTPException(
+        raise http.client.HTTPException(
             res, 'code %d reason %s' % (res.status, res.reason),
             res.getheaders(), res.read())
 
diff --git a/ryu/app/rest_conf_switch.py b/ryu/app/rest_conf_switch.py
index 62b791c6..011a407d 100644
--- a/ryu/app/rest_conf_switch.py
+++ b/ryu/app/rest_conf_switch.py
@@ -21,7 +21,7 @@ This module provides a set of REST API for switch configuration.
 Used by OpenStack Ryu agent.
 """
 
-import httplib
+import http.client
 import json
 import logging
 from webob import Response
@@ -72,7 +72,7 @@ class ConfSwitchController(ControllerBase):
         try:
             ret = func(dpid)
         except KeyError:
-            return Response(status=httplib.NOT_FOUND,
+            return Response(status=http.client.NOT_FOUND,
                             body='no dpid is found %s' %
                             dpid_lib.dpid_to_str(dpid))
 
@@ -84,7 +84,7 @@ class ConfSwitchController(ControllerBase):
             return None
 
         def _ret(_ret):
-            return Response(status=httplib.ACCEPTED)
+            return Response(status=http.client.ACCEPTED)
 
         return self._do_switch(dpid, _delete_switch, _ret)
 
@@ -104,7 +104,7 @@ class ConfSwitchController(ControllerBase):
         try:
             ret = func(dpid, key)
         except KeyError:
-            return Response(status=httplib.NOT_FOUND,
+            return Response(status=http.client.NOT_FOUND,
                             body='no dpid/key is found %s %s' %
                             (dpid_lib.dpid_to_str(dpid), key))
         return ret_func(ret)
@@ -116,7 +116,7 @@ class ConfSwitchController(ControllerBase):
             return None
 
         def _ret(_ret):
-            return Response(status=httplib.CREATED)
+            return Response(status=http.client.CREATED)
 
         return self._do_key(dpid, key, _set_val, _ret)
 
diff --git a/ryu/services/protocols/bgp/operator/commands/show/route_formatter_mixin.py b/ryu/services/protocols/bgp/operator/commands/show/route_formatter_mixin.py
index b40b1994..78b2fb33 100644
--- a/ryu/services/protocols/bgp/operator/commands/show/route_formatter_mixin.py
+++ b/ryu/services/protocols/bgp/operator/commands/show/route_formatter_mixin.py
@@ -1,4 +1,4 @@
-import StringIO
+import io
 
 
 class RouteFormatterMixin(object):
@@ -17,7 +17,7 @@ class RouteFormatterMixin(object):
 
     @classmethod
     def _format_family(cls, dest_list):
-        msg = StringIO.StringIO()
+        msg = io.StringIO()
 
         def _append_path_info(buff, path, is_best, show_prefix):
             aspath = path.get('aspath')