An outdoor unit of an air conditioner includes: a housing including a bottom surface, a side surface, and an upper surface; an outdoor heat exchanger arranged along the side surface of the housing; a blowing fan arranged on the upper surface of the housing; a bell mouth arranged around the blowing fan; a fan guard provided to cover an upper portion of the blowing fan; and a height changing member provided between the fan guard and the bell mouth and configured to change a height of the fan guard with respect to the blowing fan.