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 11:02:17 2016 +0800
@@ -230,6 +230,9 @@
         self.assertTrue(urllib.request.proxy_bypass_environment('anotherdomain.com'))
         self.assertTrue(urllib.request.proxy_bypass_environment('anotherdomain.com:8888'))
         self.assertTrue(urllib.request.proxy_bypass_environment('newdomain.com:1234'))
+        self.assertTrue(urllib.request.proxy_bypass_environment('LOCALHOST'))
+        self.assertTrue(urllib.request.proxy_bypass_environment('ANOTHERDOMAIN.COM'))
+        self.assertTrue(urllib.request.proxy_bypass_environment('NEWDOMAIN.COM:1234'))
 
 
 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 11:02:17 2016 +0800
@@ -2488,9 +2488,10 @@
     if no_proxy == '*':
         return 1
     # strip port off host
+    host = host.lower()
     hostonly, port = splitport(host)
     # check if the host ends with any of the DNS suffixes
-    no_proxy_list = [proxy.strip() for proxy in no_proxy.split(',')]
+    no_proxy_list = [proxy.strip() for proxy in no_proxy.lower().split(',')]
     for name in no_proxy_list:
         if name and (hostonly.endswith(name) or host.endswith(name)):
             return 1