Yasuhiko Kojima took up swimming while attending high school in Hiroshima. In 1936 he enrolled in Keio University. He was the Japanese Champion in the 100 metre backstroke in 1935-36 and again in 1938 as well as in the 200 backstroke in 1935 (the last time this event was held before World War II). In 1938-40 Kojima won three consecutive titles in the then rare event, 50 metre backstroke. At the 1936 Berlin Olympics he placed sixth in the final of the 100 back. During the Pacific War Kojima was assigned to the Okinawa Navy Air Corps and was killed in action in the Battle of Okinawa.