An outdoor unit of an air conditioner, including a cabinet including a base panel and a side panel; a compressor supported by the cabinet; a heat exchanger supported by the cabinet; and a leg frame at a lower end of the cabinet to support the cabinet. The leg frame includes: a channel including an upper flange coupled to the base panel, a lower flange installable on an installation surface, and a web connecting the upper flange with the lower flange. A first coupling portion and a second coupling portion are configured to fix one side portion of the channel to the side panel, and are positioned on opposite sides with the channel interposed therebetween.