Erzsi Újvári (born Erzsébet Kassák) (14 July, 1899, Érsekújvár-11 August, 1940, Moscow) was a Hungarian poet.
Her parents were Istvan Kassák and Erzsébet Istenes, and Lajos Kassák was her brother.
In 1912 she moved to Budapest and got work in a textiles factory.
Influenced by her brother she became involved in literature, and joined him in founding the avant-garde journals A Tett (1915-16) and MA.
She married the poet Sándor Barta.Along with many other avant-garde writers, she left Hungary after the fall of the Hungarian Soviet Republic.