The girls' 100 metre butterfly event at the 2018 Summer Youth Olympics took place on 11 and 12 October at the Natatorium in Buenos Aires, Argentina.

[1] The heats were started on 11 October at 11:05.

[2] The semifinals were started on 11 October at 18:12.

[3] The final was held on 12 October at 18:11.

[4]