2009 World Youth Championships in Athletics – Boys' 400 metres

The Boys' 400 metres at the 2009 World Youth Championships in Athletics was held at the Brixen-Bressanone Sport Arena on 8, 9, and 10 July. The event was won by Kirani James of the Grenada, who also won the 200 metres.

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

Kirani James set a new Championship Record and World Youth Leading in the final.

Qualification rule: first 2 of each heat (Q) plus the 4 fastest times (q) qualified.

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

Key: PB = Personal best, SB = Seasonal best

Key: PB = Personal best, SB = Seasonal best, CR = Championship record, WYL = World Youth Leading