An impeller includes a hub and a plurality of blades. The blades are arranged around the hub, and each blade includes a leading edge, a blade tip, a root portion, a trailing edge, a windward side and a leeward side. The windward side including a first turning point and a second turning point, a first vertical height difference is formed from the blade tip to the first turning point, and a second vertical height difference is formed from the first turning point to the second turning point, and the first vertical height difference is greater than the second vertical height difference. The impeller apparently reduces the noise.