The men's 100 metre backstroke event at the 2005 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	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...	53.17	Indianapolis Indianapolis Indianapolis is the capital of the U.S. state of Indiana, and the county seat of Marion County, Indiana. As of the 2010 United States Census, the city's population is 839,489. It is by far Indiana's largest city and, as of the 2010 U.S...	2 April 2005
Championship record	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	Barcelona Barcelona Barcelona is the second largest city in Spain after Madrid, and the capital of Catalonia, with a population of 1,621,537 within its administrative limits on a land area of...	22 July 2003

No new world or competition records were set during this competition.

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...		53.62
	Randall Bal Randall Bal Randall Bal is an American swimmer who specializes in the backstroke. He is a former world record holder in the 50-meter backstroke ....		54.02
	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...		54.27
4	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:* *...		54.31
5	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...		54.50
6	Aristeidis Grigoriadis Aristeidis Grigoriadis Aristeidis Grigoriadis is a Greek swimmer from Thessaloniki.-Career:Grigoriadis was the first Greek swimmer to be crowned world champion in the 50 m backstroke event of the 2005 World Championships in Montreal...		54.61
7	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...		54.81
8	Blaž Medvešek Blaž Medvešek Blaž Medvešek is a former backstroke swimmer from Slovenia, who competed for his native country of Slovenia at the 2004 Summer Olympics in Athens, Greece as well as at 2000 Summer Olympics in Sydney, Australia...		55.13