An impeller which is applied to a fan includes a hub, a plurality of first centrifugal blade and a plurality of second centrifugal blades. The hub is disposed in an accommodating space of the fan. The first centrifugal blades and the second centrifugal blades are connected to the hub. The first centrifugal blades have first ends away from the hub. The second centrifugal blades have second ends away from the hub. A distance between the second end and a center of the hub is larger than that between the first end and the hub center, and the first centrifugal blades and the second centrifugal blades are arranged periodically. Thus, an airflow noise in a constant frequency generated by the impeller can be avoided, and noises in inconstant frequency would not accumulate or generate annoying noise peak.