| 66 from 56 nations|| 50.71|
| July 29, 2011 (heats and semifinals)
July 30, 2011 (final)|
The men's 100 metre butterfly competition of the swimming events at the 2011 World Aquatics Championships was held on July 29 with the heats and the semifinals and July 30 with the final.
Swimming at the 2011 World Aquatics Championships – Men's 100 metre butterfly Wikipedia
Prior to the competition, the existing world and championship records were as follows.
66 swimmers participated in 9 heats.
The semifinals were held at 19:01.
The final was held at 18:42.