The Women's 800m Freestyle event at the 10th FINA World Aquatics Championships swam on 25–26 July 2003 in Barcelona, Spain.

Preliminary[1] heats swam during the morning session on July 25, with the top-8 finishers advancing to swim the race again in the Final[2] during the evening session on July 26.

Prior to the event, the World (WR) and Championship (CR) records were: