Swimming at the 2020 Summer Olympics – Women's 100 metre breaststroke

The women's 100 metre breaststroke event at the 2020 Summer Olympics was held from 25 July to 27 July 2021 at the Tokyo Aquatics Centre. It was the event's fourteenth consecutive appearance, having been held at every edition since 1968.

Summary
The U.S.' teen Lydia Jacoby upset South Africa's Tatjana Schoenmaker and defending champion Lilly King to capture the sprint breaststroke title. Hanging with the leaders at the turn, Jacoby broke away over the final 20 metres to win gold by almost three tenths of a second in 1:04.95. With the performance, Jacoby became just the sixth woman in history to break the 1:05 barrier. First at the turn, Schoenmaker could not contend with Jacoby's blistering final lap and settled for silver in a time of 1:05.22, 0.4 seconds shy off her Olympic record in the heats. Meanwhile, Jacoby's teammate and 2016 champion Lilly King was 0.03 seconds ahead of Jacoby at the turn but could not fend off the youngster's charge, taking bronze in 1:05.54.

ROC's Evgeniia Chikunova delivered a time of 1:05.90 to pick up the fourth spot, just ahead of teammate and defending silver medallist Yuliya Yefimova (1:06.02) by about a tenth of a second. Sweden's Sophie Hansson placed sixth in 1:06.07, while Martina Carraro (1:06.19) and Ireland's Mona McSharry (1:06.94) rounded out the championship field.

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

The following records were established during the competition:

Qualification
The Olympic Qualifying Time for the event is 1:07.07. Up to two swimmers per National Olympic Committee (NOC) can automatically qualify by swimming that time at an approved qualification event. The Olympic Selection Time is 1:09.08. Up to one swimmer per NOC meeting that time is eligible for selection, allocated by world ranking until the maximum quota for all swimming events is reached. NOCs without a female swimmer qualified in any event can also use their universality place.

Competition format
The competition consisted of three rounds: heats, semifinals, and a final. The swimmers with the best 16 times in the heats advanced to the semifinals. The swimmers with the best 8 times in the semifinals advanced to the final. Swim-offs are used as necessary to break ties for advancement to the next round.

Schedule
All times are Japan Standard Time (UTC+9)

Heats
The swimmers with the top 16 times, regardless of heat, advanced to the semifinals.

Semifinals
The swimmers with the best 8 times, regardless of heat, advanced to the final.