The men's 100 metre butterfly event at the 2003 World Aquatics Championships took place between 25 July – 26 July. Both the heats and semifinals were held on 25 July with the heats being held in the morning session and the semifinals being held in the evening session. The final was held on 26 July.

Records

Prior to the competition, the existing world and championship records were as follows.

	Name	Nationality	Time	Location	Date
World record	Michael Klim Michael Klim Michael Klim OAM is a Polish-born Australian swimmer. He was born in Gdynia. He was educated at the University High School, Melbourne and Wesley College, Melbourne where he is currently employed as the College's elite Head Coach of swimming...	Australia Australia Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...	51.81	Canberra Canberra Canberra is the capital city of Australia. With a population of over 345,000, it is Australia's largest inland city and the eighth-largest city overall. The city is located at the northern end of the Australian Capital Territory , south-west of Sydney, and north-east of Melbourne...	12 December 1999
Championship record	Lars Frölander Lars Frölander Lars Arne Frölander is a Swedish swimmer. He grew up in Ornäs in Borlänge Municipality. He competed in 5 consecutive Olympic Games . The highlight of his career was when he won the gold in the 100 metre butterfly event at the Sydney Olympic Games in 2000...	Sweden Sweden Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....	52.10	Fukuoka Fukuoka Fukuoka most often refers to the capital city of Fukuoka Prefecture.It can also refer to:-Locations:* Fukuoka, Gifu, a town in Gifu Prefecture, Japan* Fukuoka, Toyama, a town in Toyama Prefecture, Japan...	26 July 2001

The following records were established during the competition:

Date	Round	Name	Nationality	Time	WR	CR
July 25	Semifinals	Andrii Serdinov	Ukraine Ukraine Ukraine is a country in Eastern Europe. It has an area of 603,628 km², making it the second largest contiguous country on the European continent, after Russia...	51.76	WR	CR
July 25	Semifinals	Michael Phelps Michael Phelps Michael Fred Phelps is an American swimmer who has, overall, won 16 Olympic medals—six gold and two bronze at Athens in 2004, and eight gold at Beijing in 2008, becoming the most successful athlete at both of these Olympic Games editions...	United States United States The United States of America is a federal constitutional republic comprising fifty states and a federal district...	51.47	WR	CR
July 26	Final	Ian Crocker Ian Crocker Ian Lowell Crocker is a former American swimmer and five-time Olympic medalist. He is a former world record holder in the 100 meter butterfly ....	United States United States The United States of America is a federal constitutional republic comprising fifty states and a federal district...	50.98	WR	CR

Semifinals

Heat 1

Rank	Name	Nationality	Time	Notes
1	Andrii Serdinov		51.76	Q, WR
2	Ian Crocker Ian Crocker Ian Lowell Crocker is a former American swimmer and five-time Olympic medalist. He is a former world record holder in the 100 meter butterfly ....		52.21	Q
3	Thomas Rupprath Thomas Rupprath Thomas Rupprath is an Olympic swimmer from Germany, who is nicknamed "The New Albatross". A specialist in the backstroke and butterfly, especially in short course, he held the world record for the 50 m backstroke with a time of 23.27 seconds set on 31 November 2002. This was broken by Robert...		52.37	Q
4	Igor Marchenko Igor Marchenko (swimmer) Igor Yuryevich Marchenko is a Russian swimmer who competed at the 2000 and 2004 Olympics.-References:...		52.44	Q
5	Evgueni Korotychkine		52.55	Q
6	Michael Mintenko		52.57
7	Joris Keizer Joris Keizer Joris Gerhard Keizer is a retired butterfly swimmer from the Netherlands, who competed for his native country at two consecutive Summer Olympics, starting in 2000 in Sydney, Australia. There he was eliminated in the semi finals of the 100m Butterfly, and finished in fourth place with the Men's...		52.64
8	Adam Pine Adam Pine Adam Pine is an Australian freestyle and butterfly swimmer. Adam is married to Sasha Pine and is the father of 3 children, Maximillian, Buster and Xander....		53.05

Key: Q = Qualified, WR = World record

Heat 2

Rank	Name	Nationality	Time	Notes
1	Michael Phelps Michael Phelps Michael Fred Phelps is an American swimmer who has, overall, won 16 Olympic medals—six gold and two bronze at Athens in 2004, and eight gold at Beijing in 2008, becoming the most successful athlete at both of these Olympic Games editions...		51.47	Q, WR
2	Franck Esposito Franck Esposito Franck Esposito is a former swimmer from France, who won the bronze medal in the 200 metres butterfly at the 1992 Summer Olympics in Barcelona...		52.49	Q
3	Takashi Yamamoto		52.55	Q
4	Denis Sylantyev		53.12
5	Geoff Huegill Geoff Huegill Geoffrey Andrew Huegill , nicknamed Skippy and Skip, is an Australian butterfly swimmer...		53.13
6	Mattia Nalesso		53.16
7	Ioan Stefan Gherghel		53.18
8	Johannes Dietrich		53.76

Key: Q = Qualified, WR = World record

Final

Rank	Name	Nationality	Time	Notes
	Ian Crocker Ian Crocker Ian Lowell Crocker is a former American swimmer and five-time Olympic medalist. He is a former world record holder in the 100 meter butterfly ....		50.98	WR
	Michael Phelps Michael Phelps Michael Fred Phelps is an American swimmer who has, overall, won 16 Olympic medals—six gold and two bronze at Athens in 2004, and eight gold at Beijing in 2008, becoming the most successful athlete at both of these Olympic Games editions...		51.10
	Andrii Serdinov		51.59
4	Igor Marchenko Igor Marchenko (swimmer) Igor Yuryevich Marchenko is a Russian swimmer who competed at the 2000 and 2004 Olympics.-References:...		51.95
5	Thomas Rupprath Thomas Rupprath Thomas Rupprath is an Olympic swimmer from Germany, who is nicknamed "The New Albatross". A specialist in the backstroke and butterfly, especially in short course, he held the world record for the 50 m backstroke with a time of 23.27 seconds set on 31 November 2002. This was broken by Robert...		51.98
6	Takashi Yamamoto		52.27
7	Franck Esposito Franck Esposito Franck Esposito is a former swimmer from France, who won the bronze medal in the 200 metres butterfly at the 1992 Summer Olympics in Barcelona...		52.68
8	Evgueni Korotychkine		53.00

Key: WR = World record