diff --git a/pandas/core/series.py b/pandas/core/series.py
index a25178402cf6b..ea713e51e04c9 100644
--- a/pandas/core/series.py
+++ b/pandas/core/series.py
@@ -4067,7 +4067,8 @@ def apply(
             Python function or NumPy ufunc to apply.
         convert_dtype : bool, default True
             Try to find better dtype for elementwise function results. If
-            False, leave as dtype=object.
+            False, leave as dtype=object. Note that the dtype is always
+            preserved for extension array dtypes, such as Categorical.
         args : tuple
             Positional arguments passed to func after the series value.
         **kwargs