Swimming at the 2003 World Aquatics Championships – Men's 100 metre freestyle

The Men's 100 Freestyle event at the 10th FINA World Aquatics Championships swam on 23–24 July 2003 in Barcelona, Spain. Preliminary and Semifinal heats swam on July 23; while the Final swam on July 24.

Prior to the start of the event, the existing World (WR) and Championship (CR) records were:
 * WR: 47.84 by Pieter van den Hoogenband (Netherlands) swum on 19 September 2000 in Sydney, Australia
 * CR: 48.33 by Anthony Ervin (USA) swum on 27 July 2001 in Fukuoka, Japan