The women's 400 metres event at the 1998 World Junior Championships in Athletics was held in Annecy, France, at Parc des Sports on 28, 29 and 31 July.
| Gold | Natalya Nazarova | |
| Silver | Nakiya Johnson | |
| Bronze | Yudalis Díaz |
31 July
| Rank | Name | Nationality | Time | Notes | |||
|---|---|---|---|---|---|---|---|
| align=left | align=left | | 52.02 | ||||
| align=left | align=left | | 52.09 | ||||
| align=left | align=left | | 52.39 | ||||
| 4 | align=left | align=left |  | 52.89 | |||
| 5 | align=left | align=left | 53.16 | ||||
| 6 | align=left | align=left |  | 53.29 | |||
| 7 | align=left | align=left |  | 53.68 | |||
| 8 | align=left | align=left | | 54.24 |
29 July
| Rank | Name | Nationality | Time | Notes | |||
|---|---|---|---|---|---|---|---|
| 1 | align=left | align=left | | 51.95 | Q | ||
| 2 | align=left | align=left | | 52.80 | Q | ||
| 3 | align=left | align=left | | 53.01 | Q | ||
| 4 | align=left | align=left | | 53.34 | q | ||
| 5 | align=left | align=left | | 53.65 | |||
| 6 | align=left | align=left | 54.41 | ||||
| 7 | align=left | align=left |  | 54.48 | |||
| 8 | align=left | align=left | 54.70 |
| Rank | Name | Nationality | Time | Notes | |||
|---|---|---|---|---|---|---|---|
| 1 | align=left | align=left | | 52.73 | Q | ||
| 2 | align=left | align=left | | 53.07 | Q | ||
| 3 | align=left | align=left | 53.20 | Q | |||
| 4 | align=left | align=left | | 53.44 | q | ||
| 5 | align=left | align=left | 53.60 | ||||
| 6 | align=left | align=left |  | 54.34 | |||
| 7 | align=left | align=left |  | 54.51 | |||
| 8 | align=left | align=left | | 54.58 |
28 July
| Rank | Name | Nationality | Time | Notes | |||
|---|---|---|---|---|---|---|---|
| 1 | align=left | align=left | | 52.98 | Q | ||
| 2 | align=left | align=left | | 53.23 | Q | ||
| 3 | align=left | align=left | | 53.90 | Q | ||
| 4 | align=left | align=left | 54.18 | q | |||
| 5 | align=left | align=left | 54.28 | q | |||
| 6 | align=left | align=left |  | 54.69 | |||
| 7 | align=left | align=left | 55.72 |
| Rank | Name | Nationality | Time | Notes | |||
|---|---|---|---|---|---|---|---|
| 1 | align=left | align=left | | 53.07 | Q | ||
| 2 | align=left | align=left | | 53.36 | Q | ||
| 3 | align=left | align=left | | 54.00 | Q | ||
| 4 | align=left | align=left | | 54.80 | |||
| 5 | align=left | align=left | | 54.88 | |||
| 6 | align=left | align=left | | 54.96 | |||
| 7 | align=left | align=left | 55.29 |
| Rank | Name | Nationality | Time | Notes | |||
|---|---|---|---|---|---|---|---|
| 1 | align=left | align=left | 53.89 | Q | |||
| 2 | align=left | align=left | | 53.94 | Q | ||
| 3 | align=left | align=left | | 54.48 | Q | ||
| 4 | align=left | align=left | | 54.53 | q | ||
| 5 | align=left | align=left | 55.55 | ||||
| 6 | align=left | align=left |  | 57.54 |
| Rank | Name | Nationality | Time | Notes | |||
|---|---|---|---|---|---|---|---|
| 1 | align=left | align=left | | 52.74 | Q | ||
| 2 | align=left | align=left | | 53.86 | Q | ||
| 3 | align=left | align=left | | 54.13 | Q | ||
| 4 | align=left | align=left | 54.27 | q | |||
| 5 | align=left | align=left |  | 55.35 | |||
| 6 | align=left | align=left | 56.28 | ||||
| 7 | align=left | align=left | 58.92 | ||||
| 8 | align=left | align=left | 59.06 |
According to an unofficial count, 28 athletes from 21 countries participated in the event.