Swimming at the 2005 World Aquatics Championships – Men's 100 metre freestyle

The men's 100 metre freestyle at the 2005 World Aquatics Championships occurred on 27 July (heats and semifinals) and in the evening of 28 July (final) in the Olympic pool at Parc Jean-Drapeau in Montreal, Canada. 131 swimmers were entered in the event, of which 124 swam in one of 17 preliminary heats. The top-16 swimmers from the heats advanced on to semifinals; the top-8 swimmers in the two semifinals heats advanced onto the next night's final.

The existing records at the start of the event were:
 * World record (WR): 47.84, Pieter van den Hoogenband (Netherlands), September 19, 2000 in Sydney, Australia.
 * Championship record (CR): 48.33, Anthony Ervin (USA), Fukuoka 2001 (Jul.27.2001)