An electric motor includes a rotor unit disposed rotatably in a motor housing. The rotor unit includes a rotor shaft rotatable relative to the motor housing about a central axis of the motor housing, a heat conductive seat mounted with a magnet member and in sleeved relationship to an intermediate portion of the rotor shaft, and angularly spaced apart heat pipes extending through an end portion of the rotor shaft thicker than the intermediate portion and into the seat. Each heat pipe has an end portion disposed outward of the rotor shaft, and extending into and in thermal contact with a heat conductive impeller connected to the second end portion of the rotor shaft to co-rotate with the rotor shaft and covered by an outer shell cap. A stator unit is mounted fixedly in and is in thermal contact with the motor housing, and is disposed around the rotor unit.