A fan includes a frame, an impeller and a motor. The impeller includes a hub, a plurality of blades, first air-guiding plates and second air-guiding plates. The hub has a tapered shape. A width of the hub gradually increases along a direction from a top portion of the hub to a bottom portion of the hub. The hub has at least an air vent. The blades are disposed around an outer periphery of the hub. The first air-guiding plates and the second air-guiding plates are disposed around an inner periphery of the hub. The first air-guiding plates are arranged between two of the second air-guiding plates in staggered. The second air-guiding plates are arranged between two of the first air-guiding plates in staggered. The first air-guiding plates and the second air-guiding plates have different thicknesses, heights or shapes.