Rosa Valetti (17 March 1878 – 10 December 1937), born Rosa Vallentin, was a German actress, cabaret performer and singer.
Rosa Valetti was born in Berlin, the daughter of industrialist Felix Vallentin and sister of actor Hermann Vallentin. She played her first roles in the theatres of suburban Berlin. Inspired by the November Revolution and her meeting with political satirist Kurt Tucholsky, Valetti began performing in cabarets. In 1920, she founded the Café Grössenwahn ("Café Megalomania"), which has been recognized as one of the most important literary and political cabarets in 1920s Berlin. Café Megalomania was frequented by Expressionist writers, and the program of sketch comedy and political songs reflected Valetti's belief in the cabaret as an instrument of political and social criticism.
The inflation of 1919 to 1923 and the subsequent collapse of the German economy forced Valetti to close Cafe Megalomania. She directed the cabaret Rakete for a time, then launched another cafe of her own, the Rampe, which hosted the works of revolutionist poet and singer Erich Weinert. Valetti was among the founders of the floating cabaret Larifari during the late 1920s. In 1928 she performed as Mrs. Peachum in the original cast of Bertolt Brecht's Threepenny Opera, which was staged under the direction of Erich Engel at Berlin's Theater am Schiffbauerdamm.
Rosa Valetti acted in film roles from 1911. Her age and sturdy mien ensured that she acted mostly in motherly roles, as in the 1925 film Die Prinzessin und der Geiger (The Princess and the Violinist), in which she played a 46-year-old grandmother. In Josef von Sternberg's 1930 film Der Blaue Engel (The Blue Angel) she plays the wife of the magician, Kiepert (Kurt Gerron). Valetti also appears briefly in Fritz Lang's 1931 classic M as the proprietor of an underworld cafe.