| Reizo Koike | |
| Nationality: | Japanese |
| Birth Date: | 15 December 1915 |
| Birth Place: | Numazu, Shizuoka, Japan |
| Sport: | Swimming |
| Event: | 200-meter breaststroke |
| Alma Mater: | Keio University |
was a Japanese swimmer who specialized in the 200 m breaststroke. In this event he won a silver medal at the 1932 Olympics and a bronze medal at the 1936 Olympics, and set an unofficial world record in 100 m between these Olympics. During his career Koike won eight national titles.
After the end of World War II, Koike became a coach for the Japanese national Olympic swimming team and chairman of the Japan Swimming Federation. He was present in Barcelona during the 1992 Summer Olympics, when Kyoko Iwasaki won the gold medal. In 1990 Koike received the Olympic Order in Silver, and in 1996 was inducted into the International Swimming Hall of Fame. He died of lung cancer in 1998.