The women's 800 metres event at the 2004 World Junior Championships in Athletics was held in Grosseto, Italy, at Stadio Olimpico Carlo Zecchini on 13, 14 and 16 July.
| Gold | Natalya Koreyvo | |
| Silver | Simona Barcău | |
| Bronze | Kay-Ann Thompson |
16 July
| Rank | Name | Nationality | Time | Notes | |||
|---|---|---|---|---|---|---|---|
| align=left | align=left | | 2:01.47 | ||||
| align=left | align=left | | 2:02.23 | ||||
| align=left | align=left | | 2:02.67 | ||||
| 4 | align=left | align=left |  | 2:02.87 | |||
| 5 | align=left | align=left |  | 2:03.68 | |||
| 6 | align=left | align=left | | 2:04.09 | |||
| 7 | align=left | align=left | 2:05.69 | ||||
| 8 | align=left | align=left |  | 2:08.29 | |||
| 9 | align=left | align=left |  | 2:09.26 | |||
| align=left | align=left |  | DNS |
14 July
| Rank | Name | Nationality | Time | Notes | |||
|---|---|---|---|---|---|---|---|
| 1 | align=left | align=left | | 2:02.85 | Q | ||
| 2 | align=left | align=left | | 2:03.15 | Q | ||
| 3 | align=left | align=left | | 2:04.55 | Q | ||
| 4 | align=left | align=left | | 2:05.05 | q | ||
| 5 | align=left | align=left | | 2:05.13 | q | ||
| 6 | align=left | align=left | 2:05.89 | ||||
| 7 | align=left | align=left | | 2:06.16 | |||
| 8 | align=left | align=left |  | 2:09.11 |
| Rank | Name | Nationality | Time | Notes | |||
|---|---|---|---|---|---|---|---|
| 1 | align=left | align=left | | 2:06.78 | Q | ||
| 2 | align=left | align=left | | 2:06.78 | Q | ||
| 3 | align=left | align=left | | 2:06.93 | Q | ||
| 4 | align=left | align=left |  | 2:07.24 | |||
| 5 | align=left | align=left | 2:07.78 | ||||
| 6 | align=left | align=left |  | 2:09.05 | |||
| 7 | align=left | align=left | | 2:10.47 | q | ||
| 8 | align=left | align=left | 2:17.59 | q |
13 July
| Rank | Name | Nationality | Time | Notes | |||
|---|---|---|---|---|---|---|---|
| 1 | align=left | align=left | | 2:05.94 | Q | ||
| 2 | align=left | align=left | | 2:06.44 | Q | ||
| 3 | align=left | align=left | | 2:06.81 | q | ||
| 4 | align=left | align=left |  | 2:07.55 | |||
| 5 | align=left | align=left | 2:07.63 | ||||
| 6 | align=left | align=left | | 2:09.66 |
| Rank | Name | Nationality | Time | Notes | |||
|---|---|---|---|---|---|---|---|
| 1 | align=left | align=left | | 2:07.68 | Q | ||
| 2 | align=left | align=left | 2:07.93 | Q | |||
| 3 | align=left | align=left |  | 2:08.22 | |||
| 4 | align=left | align=left | 2:08.27 | ||||
| 5 | align=left | align=left | 2:09.26 | ||||
| 6 | align=left | align=left | | 2:09.36 | |||
| 7 | align=left | align=left | 2:21.15 |
| Rank | Name | Nationality | Time | Notes | |||
|---|---|---|---|---|---|---|---|
| 1 | align=left | align=left | | 2:05.46 | Q | ||
| 2 | align=left | align=left | | 2:05.49 | Q | ||
| 3 | align=left | align=left | | 2:07.17 | q | ||
| 4 | align=left | align=left |  | 2:07.56 | |||
| 5 | align=left | align=left | | 2:08.42 | |||
| 6 | align=left | align=left |  | 2:14.73 | |||
| 7 | align=left | align=left |  | 2:32.58 |
| Rank | Name | Nationality | Time | Notes | |||
|---|---|---|---|---|---|---|---|
| 1 | align=left | align=left | | 2:04.30 | Q | ||
| 2 | align=left | align=left | | 2:04.31 | Q | ||
| 3 | align=left | align=left | 2:04.34 | q | |||
| 4 | align=left | align=left | | 2:06.11 | q | ||
| 5 | align=left | align=left | | 2:06.71 | q | ||
| 6 | align=left | align=left | | 2:07.39 | q | ||
| 7 | align=left | align=left |  | 2:10.08 |
| Rank | Name | Nationality | Time | Notes | |||
|---|---|---|---|---|---|---|---|
| 1 | align=left | align=left | 2:07.10 | Q | |||
| 2 | align=left | align=left | | 2:07.32 | Q | ||
| 3 | align=left | align=left | | 2:07.93 | |||
| 4 | align=left | align=left | | 2:09.30 | |||
| 5 | align=left | align=left | | 2:09.38 | |||
| 6 | align=left | align=left |  | 2:10.85 | |||
| 7 | align=left | align=left | | 2:12.04 |
According to an unofficial count, 34 athletes from 24 countries participated in the event.