diff --git a/pandas/core/series.py b/pandas/core/series.py
index 63ef68f202a6e..6ae03f2464f76 100644
--- a/pandas/core/series.py
+++ b/pandas/core/series.py
@@ -1972,7 +1972,7 @@ def groupby(
         as_index: bool = True,
         sort: bool = True,
         group_keys: bool = True,
-        observed: bool = False,
+        observed: bool = True,
         dropna: bool = True,
     ) -> SeriesGroupBy:
         from pandas.core.groupby.generic import SeriesGroupBy