The men's 100 metre backstroke event at the 2003 World Aquatics Championships took place between 21 July – 22 July. Both the heats and semifinals were held on 21 July with the heats being held in the morning session and the semifinals being held in the evening session. The final was held on 22 July.

Records

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

	Name	Nationality	Time	Location	Date
World record	Lenny Krayzelburg Lenny Krayzelburg Lenny Krayzelburg is an American backstroke swimmer, and Olympic gold medalist and former world record holder. He swam in the 2000 and 2004 Olympics. He won a total of 4 Olympic gold medals....	United States United States The United States of America is a federal constitutional republic comprising fifty states and a federal district...	53.60	Sydney Sydney Sydney is the most populous city in Australia and the state capital of New South Wales. Sydney is located on Australia's south-east coast of the Tasman Sea. As of June 2010, the greater metropolitan area had an approximate population of 4.6 million people...	24 August 1999
Championship record	Matt Welsh Matt Welsh Matthew "Matt" Welsh is an Australian swimmer who is the former world champion in the backstroke and butterfly. Welsh trained under coach Ian Pope at the Melbourne Vicentre Club. He took two golds in 50 metres butterfly and 50 metres backstroke, during one hour, at the World Championships in...	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...	54.31	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...	23 July 2001

The following records were established during the competition:

Date	Round	Name	Nationality	Time	WR	CR
July 21	Semifinals	Aaron Peirsol Aaron Peirsol Aaron Wells Peirsol is a former American swimmer who specialized in the backstroke. He is a three-time Olympian and seven-time Olympic medalist . As part of the American team, he holds the world record in the 4×100-meter medley relay...	United States United States The United States of America is a federal constitutional republic comprising fifty states and a federal district...	54.28		CR
July 22	Final	Aaron Peirsol Aaron Peirsol Aaron Wells Peirsol is a former American swimmer who specialized in the backstroke. He is a three-time Olympian and seven-time Olympic medalist . As part of the American team, he holds the world record in the 4×100-meter medley relay...	United States United States The United States of America is a federal constitutional republic comprising fifty states and a federal district...	53.61		CR

Final

Rank	Name	Nationality	Time	Notes
	Aaron Peirsol Aaron Peirsol Aaron Wells Peirsol is a former American swimmer who specialized in the backstroke. He is a three-time Olympian and seven-time Olympic medalist . As part of the American team, he holds the world record in the 4×100-meter medley relay...		53.61	CR
	Arkady Vyatchanin Arkady Vyatchanin Arkady Arkadyevich Vyatchanin is an Russian backstroke swimmer. Vyatchanin has lived and trained in Taganrog since 1999 and is a student of the South Federal University...		53.92
	Matt Welsh Matt Welsh Matthew "Matt" Welsh is an Australian swimmer who is the former world champion in the backstroke and butterfly. Welsh trained under coach Ian Pope at the Melbourne Vicentre Club. He took two golds in 50 metres butterfly and 50 metres backstroke, during one hour, at the World Championships in...		53.92
4	Steffen Driesen Steffen Driesen Steffen Driesen is a backstroke swimmer from Germany, who competed in two consequentive Summer Olympics for his native country. At the 2004 Summer Olympics in Athens, Greece, he won the silver medal in the 4x100 Medley Relay, alongside Lars Conrad, Jens Kruppa, and Thomas Rupprath.-External...		54.17
5	Markus Rogan Markus Rogan Markus Antonius Rogan is an Austrian swimmer, who won two silver medals at the 2004 Summer Olympics in Athens, Greece and a gold medal for 200 m backstroke at the 2008 World Championships in Manchester...		54.53
6	Tomomi Morita Tomomi Morita is a backstroke swimmer from Japan. He represented his native country at the 2004 Summer Olympics in Athens, Greece. There, he won two bronze medals in the 100 m backstroke and as a member of the 4x100 m medley relay team.-References:* *...		54.86
7	László Cseh László Cseh László Cseh , is a four-time Olympic medalist Hungarian swimmer.-Personal:Cseh has competed in swimming from an early age, and has won numerous Hungarian swimming events. Cseh is coached by György Turi and Zoltán Nemes...		54.95
8	Keng Liat Alex Lim		55.18

Key: CR = Championship record