Stanisław Ruziewicz (29 August 1889 – 12 July 1941) was a Polish mathematician and one of the founders of the Lwów School of Mathematics.

He was a former student of Wacław Sierpiński, earning his doctorate in 1913 from the University of Lwów; his thesis concerned continuous functions that are not differentiable.

[1] He became a professor at the same university (then named Jan Kazimierz University) and rector of the Academy of Foreign Trade in Lwów.

[2] During the Second World War, Ruziewicz's home city of Lwów was annexed by the Ukrainian Soviet Socialist Republic, but then taken over by the General Government of German-occupied Poland in July 1941; Ruziewicz was arrested and murdered by the Gestapo on 12 July 1941 in Lwów, during the Massacre of Lwów professors.

[3] The Ruziewicz problem, asking whether the Lebesgue measure on the sphere may be characterized by certain of its properties, is named after him.