| Event: | Women's 400 metres |
| Win Label: | Winning time |
The final of the Women's 400 metres event at the 2003 Pan American Games took place on Friday August 8, 2003, with the heats staged a day earlier. Hazel-Ann Regis won the only silver medal for Grenada at the 2003 Pan American Games.
| 47.60 | October 6, 1985 | ||||
| 49.61 | August 5, 1991 |  Havana, Cuba |
| Rank | Athlete | Heats | Final | |
|---|---|---|---|---|
| Time | Rank | Time | ||
| 1 | 52.22 | 2 | 50.36 | |
| 2 | 52.21 | 1 | 51.56 | |
| 3 | 52.23 | 3 | 52.06 | |
| 4 | 52.37 | 4 | 52.23 | |
| 5 | 52.62 | 5 | 52.53 | |
| 6 | 52.76 | 7 | 52.83 | |
| 7 | 52.23 | 6 | 52.96 | |
| 8 | 53.13 | 8 | 53.26 | |
| 9 | 53.18 | 9 | ||
| 10 | 53.23 | 10 | ||
| 11 | 53.41 | 11 | ||
| 12 | 53.53 | 12 | ||
| 13 | 54.24 | 13 | ||
| 14 | 55.22 | 14 | ||
| 15 | 56.30 | 15 | ||
| 16 | 1:01.79 | 16 | ||
| - | DNF | - | ||
| - | DNS | - | ||