An outdoor unit of an air conditioner is disclosed. The outdoor unit of the air conditioner includes an outdoor unit body, a printed circuit board having a heat generating element installed thereat, an electronic box mounted in the outdoor unit body, the electronic box having the printed circuit board installed therein, a heat dissipation module contacting the heat generating element, the heat dissipation module allowing refrigerant to flow therethrough, and a heat dissipation module support mounted in the outdoor unit body such that the heat dissipation module is fixed to the heat dissipation module support to support the heat dissipation module. Shaking of the heat dissipation module can be minimized when the electronic box is separated, thereby improving reliability of the heat dissipation module.