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.
Medalists edit
| Gold | Ana Guevara Mexico
|
| Silver | Hazel-Ann Regis Grenada
|
| Bronze | Aliann Pompey Guyana
|
Records edit
| World Record |  Marita Koch (GDR) |
47.60 | October 6, 1985 |  Canberra, Australia
|
| Pan Am Record |  Ana Fidelia Quirot (CUB) |
49.61 | August 5, 1991 | Havana, Cuba
|
Results edit
| Rank | Athlete | Heats | Final | |
|---|---|---|---|---|
| Time | Rank | Time | ||
| 1 |  Ana Guevara (MEX) |
52.22 | 2 | 50.36 |
| 2 |  Hazel-Ann Regis (GRN) |
52.21 | 1 | 51.56 |
| 3 |  Aliann Pompey (GUY) |
52.23 | 3 | 52.06 |
| 4 |  Libania Grenot (CUB) |
52.37 | 4 | 52.23 |
| 5 |  Me'Lisa Barber (USA) |
52.62 | 5 | 52.53 |
| 6 |  Novlene Williams (JAM) |
52.76 | 7 | 52.83 |
| 7 | Moushami Robinson (USA) |
52.23 | 6 | 52.96 |
| 8 | Michelle Burgher (JAM) |
53.13 | 8 | 53.26 |
| 9 |  Josiane Tito (BRA) |
53.18 | 9 | |
| 10 | Geisa Coutinho (BRA) |
53.23 | 10 | |
| 11 |  Patricia Libia Rodríguez (COL) |
53.41 | 11 | |
| 12 | Mayra González (MEX) |
53.53 | 12 | |
| 13 |  Adia McKinnon (TRI) |
54.24 | 13 | |
| 14 |  Clara Hernández (DOM) |
55.22 | 14 | |
| 15 | Jackie-Ann Morain (GRN) |
56.30 | 15 | |
| 16 | Mirtha Brock (COL) |
1:01.79 | 16 | |
| — |  Eliana Pacheco (VEN) |
DNF | — | |
| — |  Tonique Williams-Darling (BAH) |
DNS | — | |