The Men's 100 metre butterfly competition of the 2018 FINA World Swimming Championships (25 m) was held on 12 and 13 December 2018 at the Hangzhou Olympic Sports Center.

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

The heats were started at 10:33.

[2] The semifinals were held at 20:22.

[3] The final was held at 20:00.