2011 World Youth Championships in Athletics – Boys' 400 metres

The Men's 400 metres at the 2011 World Youth Championships in Athletics was held at the Stadium Nord Lille Métropole on 6, 7 and 8 July.

Records
Prior to the competition, the following records were as follows.

During the competition, Arman Hall lowered his own world youth-leading 46.22 to post the second-fastest in championship history, 46.01.

Heats
Qualification rule: first 3 of each heat (Q) plus the 3 fastest times (q) qualified.

Semifinals
Qualification rule: first 2 of each heat (Q) plus the 2 fastest times (q) qualified.