diff --git a/pandas/core/series.py b/pandas/core/series.py
index aa7d108746630..43ebdc2f9dff0 100644
--- a/pandas/core/series.py
+++ b/pandas/core/series.py
@@ -3901,7 +3901,9 @@ def nlargest(
         """
         return selectn.SelectNSeries(self, n=n, keep=keep).nlargest()
 
-    def nsmallest(self, n: int = 5, keep: str = "first") -> Series:
+    def nsmallest(
+        self, n: int = 5, keep: Literal["first", "last", "all"] = "first"
+    ) -> Series:
         """
         Return the smallest `n` elements.