Merlin Ammon Ditmer (April 9, 1886 – March 10, 1950) was an American football and basketball coach.
He served as the head football coach (1920–1926) and head men's basketball coach (1920–1925) at Otterbein University in Westerville, Ohio.
Ditmer moved to Oxford, Ohio to work an assistant football and basketball coach at Miami University before serving as the school's athletic director from 1941 to 1948.