The top three runners in each of the initial nine heats automatically qualified for the second round. The next five fastest runners from across the heats also qualified. Those 32 runners competed in 4 heats in the second round, with the top fours runners from each heat qualifying for the semifinals. There were two semifinals, and only the top four from each heat advanced to the final.
<!-- The qualification period for athletics was 1 January 2003 to 9 August 2004. For the men's 100 metres, each National Olympic Committee was permitted to enter up to three athletes that had run the race in 10.21 seconds or faster during the qualification period. If an NOC had no athletes that qualified under that standard, one athlete that had run the race in 10.28 seconds or faster could be entered. -->