Aagje ("Ada") Kok (born 6 June 1947 in Amsterdam, Noord-Holland) is a former swimmer who ranked among the world's best in the butterfly stroke category during the 1960s. Her international career started in 1962 when, at the age of fifteen, she took the European title in the 100 m butterfly in Leipzig. She was also part of the silver 4×100 m medley relay team. At the Tokyo Olympics two years later she finished second in both events. She was also good at freestyle swimming, which showed when she took second place in the 400 metres at the 1966 European Championships in Utrecht. In the same tournament she also won the 100 m butterfly and the 4×100 m relay. She achieved nine world records between 1963 and 1967 in the 100 m and 200 m (not introduced until later).