Douglas John Erasmus (born 4 April 1990) is a South African swimmer who qualified to compete at the 2016 Summer Olympics held in Rio de Janeiro, Brazil.

[3] He competed at the 2013 Summer Universiade games held in Kazan, Russia, reaching the semifinals of the 50 metre freestyle.

[5][6] In both relays, he was part of South African quartets that finished seventh.

[3] At the 2016 South Africa Swimming Championships and Olympic trials, Erasmus was the fastest of over 100 competitors in the heats of the 100 metres freestyle event, setting a new personal best of 49.54 seconds.

[16][17] In May 2016, the South African Sports Confederation and Olympic Committee (SASCOC) named him as part of the South African team for the 2016 Summer Olympics held in Rio de Janeiro, Brazil, where he competed in the men's 50 metre freestyle event.