Swimming at the 2016 Summer Olympics – Men's 100 metre butterfly

The men's 100 metre butterfly event at the 2016 Summer Olympics took place on 11–12 August at the Olympic Aquatics Stadium.

In one of the most unforeseen results at the Games, Michael Phelps fell short of his attempt to fulfill an Olympic four-peat in the sprint butterfly event, due to an upset performance from Joseph Schooling, who became Singapore's first ever gold medalist. Leading from the start, Schooling defeated the field of experienced sprinters, including all-time medal leader and his personal hero Phelps, to establish a new Olympic record of 50.39 for a gold-medal triumph. Schooling did not only erase Phelps' eight-year-old record on a high-tech bodysuit by 0.19 seconds, but also produced the fastest time of the event in textile.

Three-quarters of a second later, Phelps touched the wall at the same moment as two of his rivals Chad le Clos of South Africa and four-time Olympian László Cseh of Hungary, leaving them with a matching 51.14 in a historic three-way tie for the silver. Despite missing out an Olympic title defense, Phelps also continued to ramp up his resume with his twenty-seventh career medal.

Separated the top half of the field by almost a full second, Chinese swimmer and 2014 Youth Olympic champion Li Zhuhao picked up the fifth spot with a junior world record of 51.26. Meanwhile, France's Mehdy Metella (51.58), Phelps' teammate Tom Shields (51.73), and Russia's Aleksandr Sadovnikov (51.84) closed out the championship field.

Notable swimmers failed to reach the top eight roster, featuring Schooling's countryman Quah Zheng Wen; London 2012 finalists Steffen Deibler (Germany), Joeri Verlinden (Netherlands), and Konrad Czerniak of Poland; Canada's Santo Condorelli, who produced a surprising top 16 finish from an unseeded prelims heat; and Papua New Guinea's Ryan Pini, who missed another chance to reproduce a top eight feat from Beijing 2008 in his fourth Olympic appearance.