Regan Harrison (born November 25 1977 in Brisbane, Queensland) was an Australian breaststroke swimmer of the 1990s and 2000s, who won the silver medal at the 2000 Summer Olympics in Sydney as part of the 4x100 m medley relay team.

Training at the Australian Institute of Sport, Harrison made his international debut at the 1999 Pan Pacific Championships in Sydney, where he won a silver medal in the 100 m breaststroke and came fourth in the 200 m breaststroke. The following year he finished second at the Australian Championships behind Ryan Mitchell, earning himself selection for the Sydney Olympics.

At the Olympics, he finished fourth in the 200 m breaststroke, just 0.15s slower than the bronze medal winner. After Australia's only 100 m breaststroker Phil Rogers put in a poor performance in the individual event, Australian head coach Don Talbot gambled on Harrison to replace Rogers, even though he was not originally selected in the 100 m breaststroke. Harrison combined with Matt Welsh, Geoff Huegill and Michael Klim to claim silver, behind the United States who broke the world record.

At the 2001 Australian Championships, Harrison won gold and silver respectively in the 200 m and 100 m breaststroke to qualify for the 2001 World Aquatic Championships in Fukuoka, Japan. He came sixth and 20th in the 200 m and 100 m respectively, despite setting an Australian record in the 200 m event. He combined with Welsh, Huegill and Ian Thorpe to win gold in the 4x100 m medley relay. Harrison had a poor year in 2002, managing only seventh in the 200 m breaststroke at the 2002 Commonwealth Games in Manchester, and being dropped for the 100 m event and the medley relay. He won gold and silver in the 100 m and 200 m breaststroke at the 2003 Australian Championships, but continued to decline, finishing outside the top twenty in both events at the 2001 World Aquatics Championships in Barcelona, Spain. At the 2004 Summer Olympics, Harrison was eliminated in the heats of the 200 m breaststroke. He retired after the Games.