Swimming at the 2025 World Aquatics Championships – Women's 4 × 100 metre medley relay

The United States will likely return their World Record and defending Olympic team. The team will likely be made up of Regan Smith, who holds the 100 metre backstroke world record; Gretchen Walsh, who holds the 100 metre butterfly world record; either Lilly King, or Kate Douglass on breaststroke; and Torri Huske. Projections suggest a time near 3:47.74, which would break their 3:49.63 record. Australia, silver medallists at the 2024 Olympics, will likely feature Kaylee McKeown, Sienna Toohey, and Mollie O’Callaghan, while China, led by Tang Qianting and Zhang Yufei, will challenge them for silver. Canada, Japan, France, the Netherlands, Germany, and Great Britain are expected to target finals rather than medals. ==Qualification==

Each National Federation could enter one team in the relay. The team had to be composed of swimmers who were also competing in the individual events, along with relay only swimmers who had to have met a specific qualifying time for the corresponding stroke and distance they would be swimming in the relay. Federations were only allowed to enter two relay-only swimmers for each relay they entered, though they could also enter relay-only swimmers from other relays which did not count toward this limitation. ==Records==

Prior to the competition, the existing world and championship records were as follows. The following new records were set during this competition. ==Heats==

Heats took place at 11:08. ==Final==

The final took place at 20:49. ==References==