Koichi Morishita (森下 広一; born 5 September 1967 in Yazu, Tottori) is a retired Japanese male long-distance runner. He competed for Japan at the 1992 Summer Olympics in Barcelona, Spain where he won the silver medal in the men's marathon event.
Outside of his Olympic medal, his achievements include wins at the Beppu-Ōita Marathon and the Tokyo International Marathon. His winning time in the former race (2:08:53) was the fastest marathon recorded in 1991.
He is a manager of Toyota Kyūshū Athletic team, based in Miyawaka, Fukuoka, since 1999. He has been instructing many runners including Samuel Wanjiru, who used to be a member of the team from 2005 to early 2008.