diff --git a/doc/source/whatsnew/v0.20.0.txt b/doc/source/whatsnew/v0.20.0.txt
index d76a78c68fb73..99f1bb30a0f26 100644
--- a/doc/source/whatsnew/v0.20.0.txt
+++ b/doc/source/whatsnew/v0.20.0.txt
@@ -505,11 +505,7 @@ Bug Fixes
 - Bug in ``DataFrame.to_stata()`` and ``StataWriter`` which produces incorrectly formatted files to be produced for some locales (:issue:`13856`)
 
 
-
-
-
-
-
-
 - Bug in ``DataFrame.boxplot`` where ``fontsize`` was not applied to the tick labels on both axes (:issue:`15108`)
 - Bug in ``Series.replace`` and ``DataFrame.replace`` which failed on empty replacement dicts (:issue:`15289`)
+
+- Bug in ``DataFrame.fillna()`` where the argument ``downcast`` was ignored when fillna value was of type dict instead of a scalar (:issue:`15277`)
diff --git a/pandas/core/generic.py b/pandas/core/generic.py
index 8074b167ff176..bb2664a5b8d28 100644
--- a/pandas/core/generic.py
+++ b/pandas/core/generic.py
@@ -3347,7 +3347,7 @@ def fillna(self, value=None, method=None, axis=None, inplace=False,
                     if k not in result:
                         continue
                     obj = result[k]
-                    obj.fillna(v, limit=limit, inplace=True)
+                    obj.fillna(v, limit=limit, inplace=True, downcast=downcast)
                 return result
             elif not is_list_like(value):
                 new_data = self._data.fillna(value=value, limit=limit,
diff --git a/pandas/tests/frame/test_missing.py b/pandas/tests/frame/test_missing.py
index c4f037e85edf6..aeaaa0d8a8e2b 100644
--- a/pandas/tests/frame/test_missing.py
+++ b/pandas/tests/frame/test_missing.py
@@ -252,6 +252,19 @@ def test_fillna(self):
         result = df.fillna(value={'Date': df['Date2']})
         assert_frame_equal(result, expected)
 
+    def test_fillna_downcast(self):
+        # infer int64 from float64
+        df = pd.DataFrame({'a': [1., np.nan]})
+        result = df.fillna(0, downcast='infer')
+        expected = pd.DataFrame({'a': [1, 0]})
+        assert_frame_equal(result, expected)
+
+        # infer int64 from float64 when fillna value is a dict
+        df = pd.DataFrame({'a': [1., np.nan]})
+        result = df.fillna({'a': 0}, downcast='infer')
+        expected = pd.DataFrame({'a': [1, 0]})
+        assert_frame_equal(result, expected)
+
     def test_fillna_dtype_conversion(self):
         # make sure that fillna on an empty frame works
         df = DataFrame(index=["A", "B", "C"], columns=[1, 2, 3, 4, 5])
diff --git a/pandas/tests/series/test_missing.py b/pandas/tests/series/test_missing.py
index 3c82e4ed82969..dccde42f78797 100644
--- a/pandas/tests/series/test_missing.py
+++ b/pandas/tests/series/test_missing.py
@@ -268,6 +268,19 @@ def test_datetime64tz_fillna_round_issue(self):
 
         assert_series_equal(filled, expected)
 
+    def test_fillna_downcast(self):
+        # infer int64 from float64
+        s = pd.Series([1., np.nan])
+        result = s.fillna(0, downcast='infer')
+        expected = pd.Series([1, 0])
+        assert_series_equal(result, expected)
+
+        # infer int64 from float64 when fillna value is a dict
+        s = pd.Series([1., np.nan])
+        result = s.fillna({1: 0}, downcast='infer')
+        expected = pd.Series([1, 0])
+        assert_series_equal(result, expected)
+
     def test_fillna_int(self):
         s = Series(np.random.randint(-100, 100, 50))
         s.fillna(method='ffill', inplace=True)