Born in a sporting family, his father also a competitive swimmer, Yoshihiko Osaki took up swimming at a young age while growing up in the seaside town of Wajima, Ishikawa. Competing throughout high school, Osaki did not gain national success until college. Osaki first competed internationally at the Japan-Australia dual meet in 1958, winning a silver medal in the 200 m breaststroke. In 1959, Osaki won the 200 breaststroke silver and 100 breaststroke bronze at the Japan-United States dual meet and in 1960 won the 200 breaststroke silver at the Olympic Games and helped Japan win a bronze in the medley relay. Osaki was also the Japanese 200 m breaststroke champion in 1959 and 1960.
After finishing his sporting career, Osaki became a sports administrator and official. In 1970, he became chairman of the Osaka Swimming Association and in 1987 was named chairman of the Japanese Amateur Swimming Federation. In 1984 Osaki was the founder and from 1992-2014 president of the Japanese Masters Swimming Association and was one of the organizers of the inaugural World Masters Swimming Championships held in Tokyo in 1986. Osaki was also president of Shakai Taiku Kaihata Kenkyu-Sho (Institute for Development of Physical Education), beginning in 1973, and ran a company that managed 17 swimming facilities in Japan. Osaki also acted as a swimming coach and participated at the World Masters Swimming Championships, winning seven 50 m breaststroke golds between 1986 and 2002. Osaki was inducted into the International Swimming Hall of Fame in 2006, a year after his wife Yoshiko Sato, who competed at the 1956 and 1960 Olympics and who won over 20 gold medals at the World Masters Swimming Championships. Their daughter Yoshie Osaki also became a competitive swimmer, who was selected to the Japanese 1980 Olympic team, but did not compete at the Olympics due to the boycott.
Japan