An outdoor unit for an air conditioner is disclosed. The outdoor unit according to the present invention comprises a housing which has an air inlet and an air outlet, a ventilation fan rotatably mounted in the housing, and a fan guard connected to the housing to cover the air outlet. Here, the fan guard comprises a plurality of closed ribs arranged sequentially and concentrically between a center and an outline thereof, and a plurality of radial ribs arranged in radial directions to interconnect the plurality of closed ribs, in such a manner that some of the closed ribs, which are disposed at intermediate positions near tips of the ventilation fan, are at a further distance from the ventilation fan than the other closed ribs, which are disposed near the center and the outline. Accordingly, since the fan guard is convexly raised at a position corresponding to the tips of the ventilation fan, thereby guaranteeing a predetermined space between the fan guard and the tips where the airflow is fastest, the flow resistance and the flow-induced noise can be reduced.