The men's 100 metres at the 2005 World Championships in Athletics was held at the Helsinki Olympic Stadium on August 6 and August 7. The winning margin was 0.17 seconds which as of 2024 is the greatest winning margin for the men's 100 metres at these championships. The top three runners in each of the initial eight heats automatically qualified for the second round. The next ten fastest runners from across the heats also qualified. Those 32 runners competed in four heats in the second round, with the top three runners from each heat and the single next fastest runner qualifying for the semifinals. There were two semifinal heats, and only the top four from each heat advanced to the final.

Records

Before the competition records were as follows:

Medals

Results

All times shown are in seconds. Q denotes qualification by place. q denotes qualification by time. DNS denotes did not start. DNF denotes did not finish. AR denotes area record NR denotes national record. PB denotes personal best. SB denotes season's best.

Round 1 (Heats)

Round 1 took place on 6 August, with the 62 athletes involved being split into 8 heats of 7 or 8 athletes each. The first 3 athletes in each heat ( Q ) and the next 8 fastest ( q ) qualified for the quarter-final. Wind: Heat 1: +0.6 m/s, Heat 2: +0.9 m/s, Heat 3: +0.9 m/s, Heat 4: +0.4 m/s, Heat 5: 0.0 m/s, Heat 6: +0.4 m/s, Heat 7: +0.3 m/s, Heat 8: −1.4 m/s

Round 2 (Quarter-Finals)

Round 2 took place on 6 August, with the 32 athletes involved being split into 4 heats of 8 athletes each. The first 3 athletes in each heat ( Q ) and the next 4 fastest ( q ) qualified for the semi-final. Wind: Heat 1: −2.0 m/s, Heat 2: −1.2 m/s, Heat 3: +0.7 m/s, Heat 4: −1.0 m/s

Semifinals

The semifinals took place on 7 August, with the 16 athletes involved being split into 2 heats of 8 athletes each. The first 4 athletes in each heat ( Q ) qualified for the final. Wind: Heat 1: +0.5 m/s, Heat 2: −1.0 m/s

Final

The final started at 21:35 on 7 August. Wind: +0.4 m/s