An exemplary dust-proof fan includes a frame, a stator mounted in the frame and a rotor received in the frame. The rotor includes a bracket and multiple blades pivotably mounted to the bracket. The bracket includes an inner ring and an outer ring surrounding the inner ring. Each blade has an inner pole inserted into the inner ring and an outer pole inserted into the outer ring. The blades are spaced from each other to form multiple airflow passages therebetween when the dust-proof fan is in use. The blades are overlapped with each other to close the airflow passages when the dust-proof fan is not in use.