Swimming at the 2003 World Aquatics Championships – Men's 4 × 100 metre freestyle relay

The Men's 4×100m Freestyle Relay event at the 10th FINA World Aquatics Championships swam on July 20, 2003. Preliminary heats swam in the morning session that day, with the top eight teams advancing to swim again in the Final that evening.

At the start of the event, the existing World (WR) and Championship (CR) records were:
 * WR: 3:13.67 swum by Australia on September 16, 2000 in Sydney, Australia
 * CR: 3:14.10 swum by Australia on July 22, 2001 in Fukuoka, Japan