Olszewski (feminine Olszewska, plural Olszewscy, alternative Olszowski) is a Polish surname.
The Russian-language version is Olshevsky, feminine: Olshevskaya.
The Lithuanian language forms are Olšauskas and Alšauskas, feminine: Olšauskienė/Alšauskienė (married), and Olšauskaitė/Alšauskaitė (unmarried).
Belarusian form: Альшэўскі (Alsheuski or Alshewski).
Origin could be derived from Polish word olsza or olcha, which means alder tree.