The men's 400 metres event at the 2009 Asian Athletics Championships was held at the Guangdong Olympic Stadium on November 10–11.
| width=200 bgcolor=gold | Gold | width=200 bgcolor=silver | Silver | width=200 bgcolor=CC9966 | Bronze |
| Liu Xiaosheng | Yuzo Kanemaru | Ismail Al-Sabani |
| Rank | Heat | Name | Nationality | Time | Notes | |
|---|---|---|---|---|---|---|
| 1 | 2 | 46.15 | Q | |||
| 2 | 2 | 46.17 | Q | |||
| 3 | 3 | 46.59 | Q | |||
| 4 | 3 | 46.62 | Q, SB | |||
| 5 | 2 | 46.98 | q | |||
| 6 | 3 | 47.03 | q | |||
| 7 | 1 | 47.16 | Q | |||
| 8 | 1 | 47.32 | Q | |||
| 9 | 3 | 47.47 | ||||
| 10 | 1 | 47.67 | ||||
| 11 | 2 | 47.78 | ||||
| 12 | 1 | 47.84 | ||||
| 13 | 1 | 47.88 | ||||
| 14 | 1 | 48.07 | ||||
| 15 | 1 | 48.28 | ||||
| 16 | 2 | 48.71 | ||||
| 17 | 2 | 49.00 | ||||
| 18 | 3 | 49.42 | PB | |||
| 2 | ||||||
| 3 |
| Rank | Lane | Name | Nationality | Time | Notes | |
|---|---|---|---|---|---|---|
| 4 | 46.55 | |||||
| 3 | 46.60 | |||||
| 6 | 46.84 | |||||
| 4 | 5 | 47.03 | ||||
| 5 | 1 | 47.36 | F1 | |||
| 6 | 2 | 47.41 | ||||
| 7 | 7 | 47.46 | F2 | |||
| 8 | 8 | 48.52 |