Swimming at the 2005 World Aquatics Championships – Men's 400 metre freestyle

The men's 400 metre freestyle at the 2005 World Aquatics Championships took place on 24 July (heats and final) in the Olympic pool at Parc Jean-Drapeau in Montreal, Canada. 57 swimmers were entered and in the event in the preliminary heats, the top-8 of which advanced on to swim again in the final heat that event.

The existing records at the start of the event were:
 * World record (WR): 3:40.08, Ian Thorpe (Australia), 30 July 2002 in Manchester, UK.
 * Championship record (CR): 3:40.17, Ian Thorpe (Australia), Fukuoka 2001 (22 July 2001)