Swimming at the 2009 World Aquatics Championships – Women's 4 × 100 metre medley relay

The Women's 4x100m Medley Relay at the 2009 World Aquatics Championships took place on August 1, 2009 at the Foro Italico in Rome, Italy.

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

The following records were established during the competition: