Swimming at the 2003 World Aquatics Championships – Women's 100 metre butterfly

The Women's 100m Butterfly event at the 10th FINA World Aquatics Championships swam 20–21 July 2003 in Barcelona, Spain. Preliminary heats swam in the morning session of 20 July, with the top-16 finishers advancing to semifinal heats that evening. The top-8 finishers from the Semifinals then advanced to swim again in the Final the next evening.

At the start of the event, the World (WR) and Championship (CR) records were:
 * WR: 56.61 swum by Inge de Bruijn (Netherlands) on September 17, 2000 in Sydney, Australia.
 * CR: 58.27 swum by Petria Thomas (Australia) on July 28, 2001 in Fukuoka, Japan