The men's 400 metres event at the 2005 Asian Athletics Championships was held in Incheon, South Korea on September 1–3.
| width=200 bgcolor=gold | Gold | width=200 bgcolor=silver | Silver | width=200 bgcolor=CC9966 | Bronze |
| Yuzo Kanemaru | Prasanna Amarasekara | Rohan Pradeep Kumara |
| Rank | Heat | Name | Nationality | Time | Notes | |
|---|---|---|---|---|---|---|
| 1 | 2 | 46.46 | Q | |||
| 2 | 1 | 46.56 | Q | |||
| 3 | 2 | 46.59 | Q | |||
| 4 | 1 | 46.69 | Q | |||
| 5 | 2 | 46.86 | Q | |||
| 6 | 1 | 47.10 | Q, SB | |||
| 7 | 1 | 47.13 | q, SB | |||
| 7 | 2 | 47.13 | q | |||
| 9 | 1 | 47.44 | NJR | |||
| 10 | 1 | 47.83 | ||||
| 11 | 2 | 48.06 | ||||
| 12 | 1 | 48.18 | ||||
| 13 | 2 | 48.73 | ||||
| 14 | 1 | 49.00 | ||||
| 15 | 2 | 49.20 | ||||
| 16 | 2 | 53.68 | PB |
| Rank | Name | Nationality | Time | Notes | |
|---|---|---|---|---|---|
| 46.04 | |||||
| 46.48 | |||||
| 46.52 | |||||
| 4 | 46.55 | ||||
| 5 | 46.65 | ||||
| 6 | 46.93 | ||||
| 7 | 47.58 | ||||
| 8 | 47.81 |