diff --git a/doc/source/whatsnew/v0.18.0.txt b/doc/source/whatsnew/v0.18.0.txt
index d4ed68b9f4343..a20ca31dfbdc0 100644
--- a/doc/source/whatsnew/v0.18.0.txt
+++ b/doc/source/whatsnew/v0.18.0.txt
@@ -108,7 +108,12 @@ Bug Fixes
 
 
 
-
+- Bug in ``Timedelta.round`` with negative values (:issue:`11690`)
 - Bug in ``.loc`` against ``CategoricalIndex`` may result in normal ``Index`` (:issue:`11586`)
 - Bug groupby on tz-aware data where selection not returning ``Timestamp`` (:issue:`11616`)
 - Bug in timezone info lost when broadcasting scalar datetime to ``DataFrame`` (:issue:`11682`)
+
+- Bug in ``.loc`` result with duplicated key may have ``Index`` with incorrect dtype (:issue:`11497`)
+
+- Bug in ``df.replace`` while replacing value in mixed datatype Dataframe (:issue:`11698`)
+
diff --git a/pandas/core/internals.py b/pandas/core/internals.py
index 1b08140ebec09..28c845f63f9d4 100644
--- a/pandas/core/internals.py
+++ b/pandas/core/internals.py
@@ -588,6 +588,7 @@ def replace(self, to_replace, value, inplace=False, filter=None,
         compatibility."""
 
         original_to_replace = to_replace
+        mask = isnull(self.values)
 
         # try to replace, if we raise an error, convert to ObjectBlock and retry
         try:
diff --git a/pandas/tests/test_frame.py b/pandas/tests/test_frame.py
index 5c4fa5a2e9c56..d60c5a4bd1e78 100644
--- a/pandas/tests/test_frame.py
+++ b/pandas/tests/test_frame.py
@@ -9666,6 +9666,13 @@ def test_replace(self):
         df = DataFrame(index=['a', 'b'])
         assert_frame_equal(df, df.replace(5, 7))
 
+        # GH 11698
+        # test for mixed data types.
+        df = pd.DataFrame([('-', pd.to_datetime('20150101')), ('a', pd.to_datetime('20150102'))])
+        df1 = df.replace('-', np.nan)
+        expected_df = pd.DataFrame([(np.nan, pd.to_datetime('20150101')), ('a', pd.to_datetime('20150102'))])
+        assert_frame_equal(df1, expected_df)
+
     def test_replace_list(self):
         obj = {'a': list('ab..'), 'b': list('efgh'), 'c': list('helo')}
         dfobj = DataFrame(obj)