The men's 400 metres hurdles at the 2012 World Junior Championships in Athletics was held at the Estadi Olímpic Lluís Companys on 11–13 July.
[1][2][3] Prior to the competition[update], the existing world junior and championship records were as follows.
Qualification: first 3 of each heat (Q) plus the 3 fastest times (q) qualified Qualification: The first 2 of each heat (Q) and the 2 fastest times (q) qualified According to an unofficial count, 52 athletes from 36 countries participated in the event.