Karff played in three Women's World Chess Championships: 1937 Stockholm, playing for Palestine and placing sixth (won by Vera Menchik); 1939 Buenos Aires, playing for the U.S. and placing 5th (also won by Menchik); 1949 Moscow, playing for the U.S. (won by Lyudmila Rudenko). When FIDE established titles in 1950, Mona May Karff was one of three American women to receive the title of International Woman Master.