The men's 400 metres event at the 2009 European Athletics U23 Championships was held in Kaunas, Lithuania, at S. Dariaus ir S. Girėno stadionas (Darius and Girėnas Stadium) on 16 and 17 July.
| Gold | Yannick Fonsat | |
| Silver | Nigel Levine | |
| Bronze | Jan Ciepiela |
17 July
| Rank | Name | Nationality | Time | Notes | |||
|---|---|---|---|---|---|---|---|
| align=left | align=left | | 45.68 | ||||
| align=left | align=left | 45.78 | |||||
| align=left | align=left | | 45.81 | ||||
| 4 | align=left | align=left |  | 46.13 | |||
| 5 | align=left | align=left | | 46.37 | |||
| 6 | align=left | align=left |  | 46.67 | |||
| 7 | align=left | align=left | | 46.77 | |||
| 8 | align=left | align=left | 46.84 |
16 July
Qualified: first 4 each to Final
| Rank | Name | Nationality | Time | Notes | |||
|---|---|---|---|---|---|---|---|
| 1 | align=left | align=left | | 46.42 | Q | ||
| 2 | align=left | align=left | 46.52 | Q | |||
| 3 | align=left | align=left | | 46.55 | Q | ||
| 4 | align=left | align=left | | 46.73 | Q | ||
| 5 | align=left | align=left |  | 46.75 | |||
| 6 | align=left | align=left |  | 46.89 | |||
| 7 | align=left | align=left | 46.97 | ||||
| 8 | align=left | align=left |  | 47.09 |
| Rank | Name | Nationality | Time | Notes | |||
|---|---|---|---|---|---|---|---|
| 1 | align=left | align=left | 45.86 | Q | |||
| 2 | align=left | align=left | | 46.15 | Q | ||
| 3 | align=left | align=left | | 46.31 | Q | ||
| 4 | align=left | align=left | | 46.45 | Q | ||
| 5 | align=left | align=left | 46.79 | ||||
| 6 | align=left | align=left |  | 46.84 | |||
| 7 | align=left | align=left | | 46.93 | |||
| 8 | align=left | align=left | | 47.65 |
16 July
Qualified: first 3 each heat and 4 best to Semifinals
| Rank | Name | Nationality | Time | Notes | |||
|---|---|---|---|---|---|---|---|
| 1 | align=left | align=left | 46.88 | Q | |||
| 2 | align=left | align=left | | 47.00 | Q | ||
| 3 | align=left | align=left | | 47.17 | Q | ||
| 4 | align=left | align=left | 47.62 | ||||
| 5 | align=left | align=left | | 47.65 | |||
| 6 | align=left | align=left | | 48.31 |
| Rank | Name | Nationality | Time | Notes | |||
|---|---|---|---|---|---|---|---|
| 1 | align=left | align=left | | 46.88 | Q | ||
| 2 | align=left | align=left | 47.18 | Q | |||
| 3 | align=left | align=left | | 47.24 | Q | ||
| 4 | align=left | align=left | 47.50 | ||||
| 5 | align=left | align=left |  | 48.50 | |||
| 6 | align=left | align=left |  | 49.19 | |||
| align=left | align=left |  | DNF |
| Rank | Name | Nationality | Time | Notes | |||
|---|---|---|---|---|---|---|---|
| 1 | align=left | align=left | 46.55 | Q | |||
| 2 | align=left | align=left | | 46.63 | Q | ||
| 3 | align=left | align=left | | 46.82 | Q | ||
| 4 | align=left | align=left | | 46.98 | q | ||
| 5 | align=left | align=left | | 47.36 | q | ||
| 6 | align=left | align=left |  | 47.60 |
| Rank | Name | Nationality | Time | Notes | |||
|---|---|---|---|---|---|---|---|
| 1 | align=left | align=left | | 46.66 | Q | ||
| 2 | align=left | align=left | | 46.90 | Q | ||
| 3 | align=left | align=left | | 46.96 | Q | ||
| 4 | align=left | align=left | 47.05 | q | |||
| 5 | align=left | align=left | | 47.15 | q | ||
| 6 | align=left | align=left | | 47.55 | |||
| 7 | align=left | align=left |  | 49.40 |
According to an unofficial count, 26 athletes from 19 countries participated in the event.
(1) (1) (3) (1) (1) (1) (3) (1) (1) (2) (1) (3) (1)