Swimming at the 2020 Summer Olympics – Men's 100 metre butterfly

The men's 100 metre butterfly event at the 2020 Summer Olympics was held from 29 to 31 July 2021 at the Tokyo Aquatics Centre. It was the event's fourteenth consecutive appearance, having been held at every edition since 1968.

The medals for the competition were presented by Ng Ser Miang, IOC Vice-President, Singapore; and the medalists' bouquets were presented by Dale Neuburger, FINA Treasurer; United States.

Summary
U.S. megastar Caeleb Dressel fended off a late charge by Kristóf Milák to win his second individual Olympic title in a world record of 49.45. Dressel used his signature explosive start and breakout to establish an early lead, turning first at the 50 m mark 0.65 seconds clear of the field. Though Milák closed strongly, Dressel held on for the victory and lower his world record by 5-hundredths of a second. Meanwhile Milák, the 200 m butterfly champion from earlier in the week, could not overtake Dressel but touched in a European record of 49.68 to win silver and pass Michael Phelps and Milorad Čavić to become the second fastest performer in history.

Switzerland's Noè Ponti (50.74) eclipsed his national record from the semi-finals by 0.02 seconds to claim the final spot on the podium. Tied second at the turn alongside Milák, ROC's Andrey Minakov (50.88) fell off the podium to take fourth. Matching his Polish record from the heats, Poland's Jakub Majerski (50.92) tied for fifth with Australia's Matthew Temple who could not replicate his stunning 50.45 trials performance. Guatemala's Luis Martínez touched in a national record of 51.09 to take seventh, while Bulgaria's Josif Miladinov (51.49) was a shade off his times in the earlier rounds to finish in eighth.

The medals for the competition were presented by Singapore's IOC Vice-President Ng Ser Miang, and the gifts were presented by the U.S.' FINA Treasurer Dale Neuburger.

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 51.96 seconds. 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 53.52 seconds. 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 male swimmer qualified in any event can also use their universality place.

Competition format
The competition consists of three rounds: heats, semifinals, and a final. The swimmers with the best 16 times in the heats advance to the semifinals. The swimmers with the best 8 times in the semifinals advance 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 semis, advanced to the final.