Otto Ostrowski (born 28 January 1883 in Spremberg; died 16 June 1963 in Knokke, Belgium) was a German politician of the Social Democratic Party of Germany (SPD) and Mayor of Berlin in 1946–1947.Ostrowski graduated in Romance studies and after World War I joined the SPD. From 1922 he served as mayor of Finsterwalde until he was elected mayor of the Berlin borough of Prenzlauer Berg in 1926. He held this office up to the Nazi seizure of power in 1933, when he was forced to resign.