The Girls' 400 metres at the 2017 World Youth Championships in Athletics was held on 12–14 July.
Prior to the competition, the following records were as follows.
| World Youth Best | 50.01 | Shanghai, China | 18 October 1997 | ||
| Championship Record | 51.19 | Marrakech, Morocco | 15 July 2005 | ||
| World Youth Leading | 52.05 | Sacramento, California, United States | 24 June 2017 |
Qualification rule: first 3 of each heat (Q) and the next 4 fastest qualified.[1]
| Rank | Heat | Lane | Name | Nationality | Time | Notes | |
|---|---|---|---|---|---|---|---|
| 1 | 2 | ||||||
| 1 | 3 | ||||||
| 1 | 4 | ||||||
| 1 | 5 | ||||||
| 1 | 6 | ||||||
| 1 | 7 | ||||||
| 2 | 2 | ||||||
| 2 | 3 | ||||||
| 2 | 4 | ||||||
| 2 | 5 | ||||||
| 2 | 6 | ||||||
| 2 | 7 | ||||||
| 3 | 1 | Athletes Refugee Team | |||||
| 3 | 2 | ||||||
| 3 | 3 | ||||||
| 3 | 4 | ||||||
| 3 | 5 | ||||||
| 3 | 6 | ||||||
| 3 | 7 | ||||||
| 4 | 2 | ||||||
| 4 | 3 | ||||||
| 4 | 4 | ||||||
| 4 | 5 | ||||||
| 4 | 6 | ||||||
| 4 | 7 | ||||||
| 4 | 8 |