The men's 400 metre breaststroke was a swimming event held as part of the swimming at the 1920 Summer Olympics programme.

A total of 20 swimmers from ten nations competed in the event, which was held from Sunday, August 22 to Wednesday, August 25, 1920.

These were the standing world and Olympic records (in minutes) prior to the 1920 Summer Olympics.

The fastest two in each semifinal and the faster of the two third-placed swimmer advanced to the final.

1904:  Georg Zacharias (GER)