A centrifugal blower for an air conditioner may include a centrifugal fan rotatably coupled to a motor, and a bell mouth guiding air into the centrifugal fan. The centrifugal fan may include a hub fixed to a rotary shaft of the motor, a main plate provided at an outer circumferential surface of the hub, a shroud having a suction opening surrounding the rotary shaft, the shroud positioned opposite the main plate to define a main gas flow path, and a plurality of wings arranged along the circumferential direction of the suction opening between the main plate and the shroud. A rear axial end portion of the bell mouth may be inserted into the shroud through the suction opening so as to form a predetermined radial gap with the suction opening. The rear portion of the bell mouth may include a plurality of alternately formed protruding portions and recessed portions, with the protruding portions and the recessed portions inserted into the shroud.