The men's 400 metres at the 1988 Summer Olympics in Seoul, South Korea took place between 24 and 28 September 1988. Seventy-five athletes from 55 nations competed. The maximum number of athletes per nation had been set at 3 since the 1930 Olympic Congress. The event was won by Steve Lewis of the United States, the second in what would ultimately be 7 consecutive American victories stretching from 1984 to 2008. The United States swept the podium in the event for the third time, having previously done so in 1904 and 1968.