Swimming at the 2009 World Aquatics Championships – Men's 100 metre freestyle
The men's 100 m freestyle at the 2009 World Championships took place on 29 July and the evening of 30 July at the Foro Italico in Rome, Italy.
Existing records at the start of the 2009 Championships were:
Note: During the 4×100 m freestyle relay on Sunday, 26 July 2009, the CR in the 100 m freestyle was bettered 4 times by the following lead-off legs:
- Brent Hayden, Canada — 47.77
- Stefan Nystrand, Sweden — 47.52
- César Cielo, Brazil — 47.39
- César Cielo, Brazil — 47.09
Records
The following records were established during the competition:
| Date | Round | Name | Nationality | Time | WR | CR |
| 30 July | Final | César Cielo Filho |  Brazil | 46.91 | WR | CR |
Results
Semifinals
Final
