Clasen is a German surname. Notable people with the surname include:
Alvin J. Clasen (1892–1971), American politician Daniel Clasen (1622–1678), German political theorist, religious scholar, and classicist Helmut Clasen (born 1935), German-born Canadian motorcycle racer Henry J. Clasen (1829–1907), American politician Leo Clasen (1906–1972), German Holocaust survivor