BUG: series with complex nan

pandas/_libs/lib.pyx

@@ -2485,7 +2485,14 @@ def maybe_convert_objects(ndarray[object] objects,
         elif util.is_nan(val):
             seen.nan_ = True
             mask[i] = True
-            floats[i] = complexes[i] = val
+            if util.is_complex_object(val):
+                floats[i] = fnan
+                complexes[i] = val
+                seen.complex_ = True
+                if not convert_numeric:
+                    break
+            else:
+                floats[i] = complexes[i] = val
         elif util.is_bool_object(val):
             seen.bool_ = True
             bools[i] = val

pandas/tests/generic/test_series.py

@@ -157,3 +157,8 @@ def finalize(self, other, method=None, **kwargs):
             result = pd.concat([ser, ser2])
             assert result.filename == "foo+bar"
             assert result.name is None
+
+    def test_series_with_complex_nan(self):
+        # GH#53627
+        ser = Series([complex("nan")])
+        assert np.isnan(ser[0].real) and ser[0].imag == 0