Toshihiko Seko (瀬古 利彦, Seko Toshihiko; born July 15, 1956 in Kuwana, Mie) is a Japanese former long-distance runner. He was a world-class marathon competitor in the 1980s. He represented his native country at the 1984 and the 1988 Summer Olympics in Seoul, South Korea.

Seko's notable marathon wins include Fukuoka Marathon (1978–1980, 1983), Boston Marathon (1981, 1987), London Marathon (1986) and Chicago Marathon (1986).

On March 22, 1981, Seko set world records at 25,000 m (1:13:55.8) and 30,000 m (1:29:18.8). The records stood for 30 years until they were broken by Moses Mosop in June 2011. On April 20, 1981, Seko shaved one second off Bill Rodgers's course record at the Boston Marathon.

Seko was a coach at the S & B Foods Track Team until the team was disbanded in 2012. He also was a member of the Tokyo 2016 Olympics Advisory Panel.

He serves on the Tokyo Metropolitan Government Board of Education from December 21, 2007.

He was devoted to the sport above other interests and once remarked "The marathon is my only girlfriend. I give her everything I have."