diff -uNrp a/Lib/test/test_urlparse.py b/Lib/test/test_urlparse.py
--- a/Lib/test/test_urlparse.py	2019-12-21 15:58:00.556000000 +0800
+++ b/Lib/test/test_urlparse.py	2019-12-21 15:59:11.456000000 +0800
@@ -656,6 +656,15 @@ class UrlParseTestCase(unittest.TestCase
                     with self.assertRaises(ValueError):
                         urlparse.urlsplit(url)
 
+        # check error message: invalid netloc must be formated with repr()
+        # to get an ASCII error message
+        with self.assertRaises(ValueError) as cm:
+            urlparse.urlsplit(u'http://example.com\uFF03@bing.com')
+        self.assertEqual(str(cm.exception),
+                         "netloc u'example.com\\uff03@bing.com' contains invalid characters "
+                         "under NFKC normalization")
+        self.assertIsInstance(cm.exception.args[0], str)
+
 def test_main():
     test_support.run_unittest(UrlParseTestCase)
 
diff -uNrp a/Lib/urlparse.py b/Lib/urlparse.py
--- a/Lib/urlparse.py	2019-12-21 15:58:00.480000000 +0800
+++ b/Lib/urlparse.py	2019-12-21 15:59:55.128000000 +0800
@@ -181,8 +181,9 @@ def _checknetloc(netloc):
     _, _, netloc = netloc.rpartition('@') # anything to the left of '@' is okay
     for c in '/?#@:':
         if c in netloc2:
-            raise ValueError(u"netloc '" + netloc + u"' contains invalid " +
-                             u"characters under NFKC normalization")
+            raise ValueError("netloc %r contains invalid characters "
+                             "under NFKC normalization"
+                             % netloc)
 
 def urlsplit(url, scheme='', allow_fragments=True):
     """Parse a URL into 5 components:
diff -uNrp a/Misc/NEWS.d/next/Library/2019-06-10-12-02-45.bpo-36742.UEdHXJ.rst b/Misc/NEWS.d/next/Library/2019-06-10-12-02-45.bpo-36742.UEdHXJ.rst
--- a/Misc/NEWS.d/next/Library/2019-06-10-12-02-45.bpo-36742.UEdHXJ.rst	1970-01-01 08:00:00.000000000 +0800
+++ b/Misc/NEWS.d/next/Library/2019-06-10-12-02-45.bpo-36742.UEdHXJ.rst	2019-12-21 16:00:40.480000000 +0800
@@ -0,0 +1,3 @@
+:func:`urlparse.urlsplit` error message for invalid ``netloc`` according to
+NFKC normalization is now a :class:`str` string, rather than a
+:class:`unicode` string, to prevent error when displaying the error.
