Heats
vendredi 10 août 2018, 03h00 GMT – 03h00 GMT
| Nom | Équipe | Temps | |
|---|---|---|---|
| 1 |  Kylie Masse | Canada | 58.29″ |
| 2 |  Kathleen Baker | United States | + 0.12″ |
| 3 |  Emily Seebohm | Australia | + 0.5″ |
| 4 |  Regan Smith | United States | + 0.98″ |
| 5 |  Natsumi Sakai | Japan | + 1.16″ |
| 6 | Olivia Smoliga | United States | + 1.18″ |
| 7 | Kaylee McKeown | Australia | + 1.62″ |
| 8 | Anna Konishi | Japan | + 2.01″ |
| 9 | Kennedy Goss | Canada | + 2.64″ |
| 10 | Isabella Arcila | Colombia | + 3.25″ |
| 11 | Ali Galyer | New Zealand | + 3.32″ |
| 12 | Danielle Hanus | Canada | + 3.49″ |
| 13 | Yifan Yang | China | + 3.91″ |
| 14 | Chloe Isleta | Philippines | + 6.79″ |
| 15 | Gianna Vivien Garcia | Philippines | + 14.64″ |
| 16 | Osisang Chilton | Palau | + 20.25″ |
| McKenna DeBever | Peru | DQ | |
| Taylor Ruck | Canada | DNS | |
| Sayaka Akase | Japan | DNS |