The men's 400 metres hurdles event at the 1986 World Junior Championships in Athletics was held in Athens, Greece, at Olympic Stadium on 16, 17 and 18 July.
| Gold | Emilio Valle | |
| Silver | Hiroshi Kakimori | |
| Bronze | Pascal Maran |
18 July
| Rank | Name | Nationality | Time | Notes | |||
|---|---|---|---|---|---|---|---|
| align=left | align=left | | 50.02 | ||||
| align=left | align=left | | 50.09 | ||||
| align=left | align=left | | 50.39 | ||||
| 4 | align=left | align=left | 50.58 | ||||
| 5 | align=left | align=left |  | 50.67 | |||
| 6 | align=left | align=left | 50.87 | ||||
| 7 | align=left | align=left |  | 51.69 | |||
| align=left | align=left |  | DNF |
17 July
| Rank | Name | Nationality | Time | Notes | |||
|---|---|---|---|---|---|---|---|
| 1 | align=left | align=left | | 50.05 | Q | ||
| 2 | align=left | align=left | | 50.39 | Q | ||
| 3 | align=left | align=left | | 50.51 | Q | ||
| 4 | align=left | align=left | 50.57 | Q | |||
| 5 | align=left | align=left | | 51.90 | |||
| 6 | align=left | align=left |  | 52.38 | |||
| 7 | align=left | align=left |  | 53.17 | |||
| align=left | align=left | DNS |
| Rank | Name | Nationality | Time | Notes | |||
|---|---|---|---|---|---|---|---|
| 1 | align=left | align=left | | 50.27 | Q | ||
| 2 | align=left | align=left | | 50.72 | Q | ||
| 3 | align=left | align=left | | 50.99 | Q | ||
| 4 | align=left | align=left | 51.12 | Q | |||
| 5 | align=left | align=left |  | 51.23 | |||
| 6 | align=left | align=left |  | 52.38 | |||
| 7 | align=left | align=left | | 53.22 | |||
| align=left | align=left |  | DNS |
16 July
| Rank | Name | Nationality | Time | Notes | |||
|---|---|---|---|---|---|---|---|
| 1 | align=left | align=left | | 50.70 | Q | ||
| 2 | align=left | align=left | | 51.29 | Q | ||
| 3 | align=left | align=left | | 52.28 | Q | ||
| 4 | align=left | align=left |  | 52.64 | |||
| 5 | align=left | align=left |  | 53.02 | |||
| 6 | align=left | align=left |  | 54.78 | |||
| 7 | align=left | align=left | 57.30 |
| Rank | Name | Nationality | Time | Notes | |||
|---|---|---|---|---|---|---|---|
| 1 | align=left | align=left | | 51.12 | Q | ||
| 2 | align=left | align=left | 51.48 | Q | |||
| 3 | align=left | align=left | | 51.62 | Q | ||
| 4 | align=left | align=left | | 52.01 | q | ||
| 5 | align=left | align=left | | 52.89 | |||
| 6 | align=left | align=left |  | 52.99 | |||
| 7 | align=left | align=left | 53.85 |
| Rank | Name | Nationality | Time | Notes | |||
|---|---|---|---|---|---|---|---|
| 1 | align=left | align=left | | 51.90 | Q | ||
| 2 | align=left | align=left | 52.20 | Q | |||
| 3 | align=left | align=left | | 52.29 | Q | ||
| 4 | align=left | align=left |  | 52.42 | |||
| 5 | align=left | align=left | 52.48 | ||||
| 6 | align=left | align=left |  | 53.96 | |||
| 7 | align=left | align=left | 55.30 |
| Rank | Name | Nationality | Time | Notes | |||
|---|---|---|---|---|---|---|---|
| 1 | align=left | align=left | | 50.61 | Q | ||
| 2 | align=left | align=left | | 51.12 | Q | ||
| 3 | align=left | align=left | | 52.41 | Q | ||
| 4 | align=left | align=left | 53.19 | ||||
| 5 | align=left | align=left | | 53.41 | |||
| 6 | align=left | align=left | 55.12 | ||||
| 7 | align=left | align=left |  | 56.15 | |||
| 8 | align=left | align=left | 56.38 |
| Rank | Name | Nationality | Time | Notes | |||
|---|---|---|---|---|---|---|---|
| 1 | align=left | align=left | | 51.93 | Q | ||
| 2 | align=left | align=left | 52.04 | Q | |||
| 3 | align=left | align=left | | 52.14 | Q | ||
| 4 | align=left | align=left | | 52.60 | |||
| 5 | align=left | align=left | 52.63 | ||||
| 6 | align=left | align=left |  | 54.66 | |||
| 7 | align=left | align=left | | 54.73 | |||
| 8 | align=left | align=left | 59.14 |
According to an unofficial count, 37 athletes from 28 countries participated in the event.