An apparatus for suctioning external air of a clothes dryer, comprises a housing provided at one side with a suction port for introducing external air; a fan installed at the housing and generating a suction force for sucking external air while being rotated; a driving motor driving the fan; a guide duct guiding the external air introduced from the suction port to a condenser; and a grille installed at a predetermined gap from one side face of the housing where the suction port is to be installed so that a channel can be formed between the grille and the one side face and comprised of a plurality of grille plates extending in a direction lengthwise of the grille, one widthwise ends of the grille plates being bent toward the suction port. Accordingly, the apparatus has advantages such as a decrease in flow resistance, an improvement of a condensing effect and a decrease of vibration and noise by setting the flow amount and flow velocity of a cooling air to be suctioned in the best condition.