Swimming at the 2009 World Aquatics Championships – Women's 100 metre butterfly

The first heats of the Women's 100 m Butterfly took place on the morning of Sunday, 26 July. The semi-final took place in the evening session of 26 July and the final took place on the evening of 27 July at the Foro Italico in Rome, Italy. In the final, 7 of the 8 swimmers finished within the same second, and 5 within the same 0.1 of a second.

Records
Prior to this competition, the existing world and competition records were as follows:

The following records were established during the competition:

Heats
Key: CR = Championship record, NR = National record

Finals
Note: The Dutch Record in this event is Inge de Bruijn's former World Record (56.61), which may help to explain why Veldhuis was the only finalist not to set a National Record (NR).