An outdoor unit of an air conditioner may include a case that forms an outside air inlet; a barrier that partitions an inside of the case into a heat exchange space and an electric space; a heat exchanger disposed in the heat exchange space; a fan disposed in the heat exchange space; a compressor disposed in the electric space; and a control box assembly disposed in the electric space. The control box assembly may include a control box connected to the outside air inlet and having electric components disposed therein; and a heat dissipation duct connected to an inside of the control box and that extends from one side of the control box to the barrier. The air introduced through the outside air inlet may be discharged to the heat exchange space after passing through the control box and the heat dissipation duct.