The men's 400 metres hurdles event at the 1988 World Junior Championships in Athletics was held in Sudbury, Ontario, Canada, at Laurentian University Stadium on 27, 28 and 29 July.
| Gold | Kelly Carter | |
| Silver | Mugur Mateescu | |
| Bronze | Vadim Zadoynov |
29 July
| Rank | Name | Nationality | Time | Notes | |||
|---|---|---|---|---|---|---|---|
| align=left | align=left | | 49.50 | ||||
| align=left | align=left | | 50.70 | ||||
| align=left | align=left | 50.88 | |||||
| 4 | align=left | align=left | | 51.01 | |||
| 5 | align=left | align=left | 51.70 | ||||
| 6 | align=left | align=left | 51.78 | ||||
| 7 | align=left | align=left | 52.23 | ||||
| 8 | align=left | align=left |  | 52.40 |
28 July
| Rank | Name | Nationality | Time | Notes | |||
|---|---|---|---|---|---|---|---|
| 1 | align=left | align=left | | 50.76 | Q | ||
| 2 | align=left | align=left | | 51.31 | Q | ||
| 3 | align=left | align=left | 51.51 | Q | |||
| 4 | align=left | align=left | 51.74 | q | |||
| 5 | align=left | align=left |  | 51.93 | |||
| 6 | align=left | align=left | | 52.44 | |||
| 7 | align=left | align=left | 52.86 | ||||
| align=left | align=left |  | DQ |
| Rank | Name | Nationality | Time | Notes | |||
|---|---|---|---|---|---|---|---|
| 1 | align=left | align=left | | 50.99 | Q | ||
| 2 | align=left | align=left | 51.56 | Q | |||
| 3 | align=left | align=left | | 51.62 | Q | ||
| 4 | align=left | align=left | 51.63 | q | |||
| 5 | align=left | align=left |  | 52.72 | |||
| 6 | align=left | align=left |  | 52.73 | |||
| 7 | align=left | align=left | | 54.54 | |||
| 8 | align=left | align=left |  | 55.31 |
27 July
| Rank | Name | Nationality | Time | Notes | |||
|---|---|---|---|---|---|---|---|
| 1 | align=left | align=left | 51.80 | Q | |||
| 2 | align=left | align=left | 51.89 | Q | |||
| 3 | align=left | align=left | 51.90 | Q | |||
| 4 | align=left | align=left | | 52.11 | q | ||
| 5 | align=left | align=left | | 53.18 | q | ||
| 6 | align=left | align=left | 54.20 | ||||
| 7 | align=left | align=left |  | 54.21 |
| Rank | Name | Nationality | Time | Notes | |||
|---|---|---|---|---|---|---|---|
| 1 | align=left | align=left | 51.90 | Q | |||
| 2 | align=left | align=left | | 52.19 | Q | ||
| 3 | align=left | align=left | 52.99 | Q | |||
| 4 | align=left | align=left |  | 53.25 | |||
| 5 | align=left | align=left |  | 53.56 | |||
| 6 | align=left | align=left | 53.88 | ||||
| 7 | align=left | align=left |  | 55.80 | |||
| 8 | align=left | align=left | 56.30 |
| Rank | Name | Nationality | Time | Notes | |||
|---|---|---|---|---|---|---|---|
| 1 | align=left | align=left | | 52.02 | Q | ||
| 2 | align=left | align=left | | 52.39 | Q | ||
| 3 | align=left | align=left | | 52.57 | Q | ||
| 4 | align=left | align=left | | 52.79 | q | ||
| 5 | align=left | align=left |  | 53.38 | |||
| 6 | align=left | align=left | | 53.48 | |||
| 7 | align=left | align=left |  | 55.24 | |||
| 8 | align=left | align=left | 60.76 |
| Rank | Name | Nationality | Time | Notes | |||
|---|---|---|---|---|---|---|---|
| 1 | align=left | align=left | | 51.20 | Q | ||
| 2 | align=left | align=left | | 52.54 | Q | ||
| 3 | align=left | align=left | | 52.70 | Q | ||
| 4 | align=left | align=left | | 52.75 | q | ||
| 5 | align=left | align=left | 53.31 | ||||
| 6 | align=left | align=left | 53.84 |
According to an unofficial count, 29 athletes from 24 countries participated in the event.