diff --git a/doc/source/whatsnew/v0.23.0.txt b/doc/source/whatsnew/v0.23.0.txt
index 09bd09b06d9b9..ca46f94752731 100644
--- a/doc/source/whatsnew/v0.23.0.txt
+++ b/doc/source/whatsnew/v0.23.0.txt
@@ -1165,3 +1165,4 @@ Other
 
 - Improved error message when attempting to use a Python keyword as an identifier in a ``numexpr`` backed query (:issue:`18221`)
 - Bug in accessing a :func:`pandas.get_option`, which raised ``KeyError`` rather than ``OptionError`` when looking up a non-existant option key in some cases (:issue:`19789`)
+- Bug in :func:`assert_series_equal` and :func:`assert_frame_equal` for Series or DataFrames with differing unicode data (:issue:`20503`)
diff --git a/pandas/tests/util/test_testing.py b/pandas/tests/util/test_testing.py
index 1c878604b11a2..d6f58d16bcf64 100644
--- a/pandas/tests/util/test_testing.py
+++ b/pandas/tests/util/test_testing.py
@@ -290,6 +290,24 @@ def test_numpy_array_equal_message(self):
             assert_almost_equal(np.array([1, 2]), np.array([3, 4, 5]),
                                 obj='Index')
 
+    def test_numpy_array_equal_unicode_message(self):
+        # Test ensures that `assert_numpy_array_equals` raises the right
+        # exception when comparing np.arrays containing differing
+        # unicode objects (#20503)
+
+        expected = """numpy array are different
+
+numpy array values are different \\(33\\.33333 %\\)
+\\[left\\]:  \\[á, à, ä\\]
+\\[right\\]: \\[á, à, å\\]"""
+
+        with tm.assert_raises_regex(AssertionError, expected):
+            assert_numpy_array_equal(np.array([u'á', u'à', u'ä']),
+                                     np.array([u'á', u'à', u'å']))
+        with tm.assert_raises_regex(AssertionError, expected):
+            assert_almost_equal(np.array([u'á', u'à', u'ä']),
+                                np.array([u'á', u'à', u'å']))
+
     @td.skip_if_windows
     def test_numpy_array_equal_object_message(self):
 
@@ -499,10 +517,13 @@ def _assert_not_equal(self, a, b, **kwargs):
     def test_equal(self):
         self._assert_equal(Series(range(3)), Series(range(3)))
         self._assert_equal(Series(list('abc')), Series(list('abc')))
+        self._assert_equal(Series(list(u'áàä')), Series(list(u'áàä')))
 
     def test_not_equal(self):
         self._assert_not_equal(Series(range(3)), Series(range(3)) + 1)
         self._assert_not_equal(Series(list('abc')), Series(list('xyz')))
+        self._assert_not_equal(Series(list(u'áàä')), Series(list(u'éèë')))
+        self._assert_not_equal(Series(list(u'áàä')), Series(list(b'aaa')))
         self._assert_not_equal(Series(range(3)), Series(range(4)))
         self._assert_not_equal(
             Series(range(3)), Series(
@@ -678,6 +699,49 @@ def test_frame_equal_message(self):
                                pd.DataFrame({'A': [1, 2, 3], 'B': [4, 5, 7]}),
                                by_blocks=True)
 
+    def test_frame_equal_message_unicode(self):
+        # Test ensures that `assert_frame_equals` raises the right
+        # exception when comparing DataFrames containing differing
+        # unicode objects (#20503)
+
+        expected = """DataFrame\\.iloc\\[:, 1\\] are different
+
+DataFrame\\.iloc\\[:, 1\\] values are different \\(33\\.33333 %\\)
+\\[left\\]:  \\[é, è, ë\\]
+\\[right\\]: \\[é, è, e̊\\]"""
+
+        with tm.assert_raises_regex(AssertionError, expected):
+            assert_frame_equal(pd.DataFrame({'A': [u'á', u'à', u'ä'],
+                                             'E': [u'é', u'è', u'ë']}),
+                               pd.DataFrame({'A': [u'á', u'à', u'ä'],
+                                             'E': [u'é', u'è', u'e̊']}))
+
+        with tm.assert_raises_regex(AssertionError, expected):
+            assert_frame_equal(pd.DataFrame({'A': [u'á', u'à', u'ä'],
+                                             'E': [u'é', u'è', u'ë']}),
+                               pd.DataFrame({'A': [u'á', u'à', u'ä'],
+                                             'E': [u'é', u'è', u'e̊']}),
+                               by_blocks=True)
+
+        expected = """DataFrame\\.iloc\\[:, 0\\] are different
+
+DataFrame\\.iloc\\[:, 0\\] values are different \\(100\\.0 %\\)
+\\[left\\]:  \\[á, à, ä\\]
+\\[right\\]: \\[a, a, a\\]"""
+
+        with tm.assert_raises_regex(AssertionError, expected):
+            assert_frame_equal(pd.DataFrame({'A': [u'á', u'à', u'ä'],
+                                             'E': [u'é', u'è', u'ë']}),
+                               pd.DataFrame({'A': ['a', 'a', 'a'],
+                                             'E': ['e', 'e', 'e']}))
+
+        with tm.assert_raises_regex(AssertionError, expected):
+            assert_frame_equal(pd.DataFrame({'A': [u'á', u'à', u'ä'],
+                                             'E': [u'é', u'è', u'ë']}),
+                               pd.DataFrame({'A': ['a', 'a', 'a'],
+                                             'E': ['e', 'e', 'e']}),
+                               by_blocks=True)
+
 
 class TestAssertCategoricalEqual(object):
 
diff --git a/pandas/util/testing.py b/pandas/util/testing.py
index 6e13a17eba68c..e1484a9c1b390 100644
--- a/pandas/util/testing.py
+++ b/pandas/util/testing.py
@@ -38,7 +38,7 @@
 import pandas.compat as compat
 from pandas.compat import (
     filter, map, zip, range, unichr, lrange, lmap, lzip, u, callable, Counter,
-    raise_with_traceback, httplib, StringIO, PY3)
+    raise_with_traceback, httplib, StringIO, string_types, PY3, PY2)
 
 from pandas import (bdate_range, CategoricalIndex, Categorical, IntervalIndex,
                     DatetimeIndex, TimedeltaIndex, PeriodIndex, RangeIndex,
@@ -992,11 +992,20 @@ def raise_assert_detail(obj, message, left, right, diff=None):
         left = pprint_thing(left)
     elif is_categorical_dtype(left):
         left = repr(left)
+
+    if PY2 and isinstance(left, string_types):
+        # left needs to be printable in native text type in python2
+        left = left.encode('utf-8')
+
     if isinstance(right, np.ndarray):
         right = pprint_thing(right)
     elif is_categorical_dtype(right):
         right = repr(right)
 
+    if PY2 and isinstance(right, string_types):
+        # right needs to be printable in native text type in python2
+        right = right.encode('utf-8')
+
     msg = """{obj} are different
 
 {message}