| Merlin Ditmer | |
| Birth Date: | 9 April 1886 |
| Birth Place: | Potsdam, Ohio, U.S. |
| Death Place: | Cincinnati, Ohio, U.S. |
| Alma Mater: | Otterbein |
| Coach Sport1: | Football |
| Coach Years2: | 1920–1926 |
| Coach Team2: | Otterbein |
| Coach Years3: | 1927–1940 |
| Coach Team3: | Miami (OH) (assistant) |
| Coach Sport4: | Basketball |
| Coach Years5: | 1920–1925 |
| Coach Team5: | Otterbein |
| Coach Years6: | 1927–1941 |
| Coach Team6: | Miami (OH) (assistant) |
| Admin Years1: | 1941–1948 |
| Admin Team1: | Miami (OH) |
| Overall Record: | 13–37–4 (football) 6–25 (basketball) |
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.[1] 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.[2]