The boys' 100 metre butterfly event at the 2018 Summer Youth Olympics took place on 8 and 9 October at the Natatorium in Buenos Aires, Argentina.

[1] The heats were started on 8 October at 10:30.

[2] The semifinals were started on 8 October at 18:32.

[3] The swim-off was held on 9 October at 11:29.

[4] The final was held on 9 October at 18:46.