Stanisław Kętrzyński (Polish pronunciation: [staˈɲiswaf kɛnˈtʂɨɲskʲi]; September 10, 1878 in Lwów, Austrian Empire – May 26, 1950 in Warsaw, Poland) was a Polish historian and diplomat.
He was the son of Wojciech Kętrzyński from Lötzen (Lec), East Prussia, an Austrian citizen with Kashubian and Masurian ancestors, who became a Polish scholar.
During the Second World War Stanisław Kętrzyński was a prisoner in the German concentration camp Auschwitz.
Among his students were Stanisław Arnold, Aleksander Gieysztor, Jadwiga Karwasińska and Adam Wolff.