2012 World Junior Championships in Athletics – Women's 400 metres hurdles

The women's 400 metres hurdles at the 2012 World Junior Championships in Athletics was held at the Estadi Olímpic Lluís Companys on 12, 13, and 14 July.

Prior to the competition^[update], the existing world junior and championship records were as follows.

Qualification: first 4 of each heat (Q) plus the 4 fastest times (q) qualified

Qualification: The first 2 of each heat (Q) and the 2 fastest times (q) qualified

According to an unofficial count, 36 athletes from 26 countries participated in the event.