A drain pump is provided that may include a pump motor; an impeller connected to a rotational shaft of the pump motor. The impeller may include a circular hub, an impeller shaft that extends from a center of a lower surface of the hub, and a plurality of blades that extends from an outer circumferential surface of the impeller shaft and the lower surface of the hub in a radial direction of the hub. The hub may have a longitudinal cross section in which a thickness of the hub gradually increases from the center of the lower surface toward an edge thereof.