Castner is a German surname. Notable people with the surname include:
Caspar Castner (1655–1709), German Roman Catholic missionary Eugene Castner Lewis (1845–1917), American engineer and businessman Hamilton Castner (1858–1899), American industrial chemist Joseph Compton Castner (1869–1946), American general Lawrence V. Castner (1902–1949), American businessman, fencer and military officer Michael Castner, American journalist Paul Castner (1897–1986), American baseball player