diff -r f4c6dab59cd8 Lib/test/test_urllib.py
--- a/Lib/test/test_urllib.py	Tue Apr 26 17:04:18 2016 +0200
+++ b/Lib/test/test_urllib.py	Wed Apr 27 17:07:14 2016 +0800
@@ -231,6 +231,18 @@
         self.assertTrue(urllib.request.proxy_bypass_environment('anotherdomain.com:8888'))
         self.assertTrue(urllib.request.proxy_bypass_environment('newdomain.com:1234'))
 
+    def test_proxy_bypass_environment_host_match(self):
+        bypass = urllib.request.proxy_bypass_environment
+        self.env.set('NO_PROXY', 'localhost, anotherdomain.com, newdomain.com:1234')
+        self.assertTrue(bypass('localhost'))
+        self.assertTrue(bypass('LocalHost'))                 # MixedCase
+        self.assertTrue(bypass('LOCALHOST'))                 # UPPERCASE
+        self.assertTrue(bypass('newdomain.com:1234'))
+        self.assertTrue(bypass('anotherdomain.com:8888'))
+        self.assertTrue(bypass('www.newdomain.com:1234'))
+        self.assertFalse(bypass('prelocalhost'))
+        self.assertFalse(bypass('newdomain.com'))            # no port
+        self.assertFalse(bypass('newdomain.com:1235'))       # wrong port
 
 class ProxyTests_withOrderedEnv(unittest.TestCase):
 
diff -r f4c6dab59cd8 Lib/urllib/request.py
--- a/Lib/urllib/request.py	Tue Apr 26 17:04:18 2016 +0200
+++ b/Lib/urllib/request.py	Wed Apr 27 17:07:14 2016 +0800
@@ -2492,8 +2492,11 @@
     # check if the host ends with any of the DNS suffixes
     no_proxy_list = [proxy.strip() for proxy in no_proxy.split(',')]
     for name in no_proxy_list:
-        if name and (hostonly.endswith(name) or host.endswith(name)):
-            return 1
+        if name:
+            name = re.escape(name)
+            pattern = '(.+\\.)?%s$' % name
+            if re.match(pattern, hostonly, re.I) or re.match(pattern, host, re.I):
+                return 1
     # otherwise, don't bypass
     return 0