Heats
vendredi 10 août 2018, 03h00 GMT – 03h00 GMT
| Nom | Équipe | Temps | |
|---|---|---|---|
| 1 |  Simone Manuel | United States | 53.23″ |
| 2 |  Cate Campbell | Australia | + 0.04″ |
| 3 |  Mallory Comerford | United States | + 0.07″ |
| 4 |  Taylor Ruck | Canada | + 0.11″ |
| 5 | Shayna Jack | Australia | + 0.38″ |
| 6 | Emma McKeon | Australia | + 0.74″ |
| 7 | Kayla Sanchez | Canada | + 0.79″ |
| 7 | Margo Geer | United States | + 0.79″ |
| 9 | Kelsi Dahlia | United States | + 0.86″ |
| 10 | Katie McLaughlin | United States | + 0.91″ |
| 10 |  Rikako Ikee | Japan | + 0.91″ |
| 12 | Madeline Groves | Australia | + 0.95″ |
| 13 | Abbey Weitzeil | United States | + 0.97″ |
| 14 | Allison Schmitt | United States | + 1.3″ |
| 15 | Rebecca Smith | Canada | + 1.31″ |
| 16 |  Larissa Oliveira | Brazil | + 1.45″ |
| 17 | Tomomi Aoki | Japan | + 1.61″ |
| 18 | Alexia Zevnik | Canada | + 1.7″ |
| 18 | Brianna Throssell | Australia | + 1.7″ |
| 20 | Chihiro Igarashi | Japan | + 1.73″ |
| 21 | Gabrielle Deloof | United States | + 1.99″ |
| 22 | Mayuka Yamamoto | Japan | + 2.09″ |
| 23 | Kyla Leibel | Canada | + 2.14″ |
| 24 | Rio Shirai | Japan | + 2.21″ |
| 25 | Sarah Fournier | Canada | + 2.34″ |
| 26 | Yui Yamane | Japan | + 2.5″ |
| 27 | Cristina Lorrane | Brazil | + 3.27″ |
| 28 | Ai Soma | Japan | + 3.9″ |
| 29 | Nicole Oliva | Philippines | + 3.94″ |
| 30 | Miranda Cristina Renner | Philippines | + 6.82″ |
| 31 | Mineri Gomez | Guam | + 11.17″ |
| 32 | Gianna Vivien Garcia | Philippines | + 11.31″ |
| 33 | Osisang Chilton | Palau | + 14.07″ |
| Kanako Watanabe | Japan | DNS | |
| Ariarne Titmus | Australia | DNS |