A heat radiation unit is disclosed. The heat radiation unit includes a heat radiation member thermally connected to a heat source, to radiate heat generated from the heat source, a refrigerant pipe thermally connected to the heat radiation member while being formed therein with a channel, through which refrigerant flows, a pipe jacket coupled to the heat radiation member, and formed with a receiving groove to receive a portion of the refrigerant pipe, and a cover bracket to press the portion of the refrigerant pipe received in the receiving groove of the pipe jacket in a downward direction of the receiving groove. An outdoor unit of an air conditioner is also disclosed. The outdoor unit includes a case to form an appearance of the outdoor unit, a heat source disposed in the case, and the heat radiation unit connected to the heat source, to radiate heat from the heat source.