A centrifugal blower includes a casing, a motor fixed in the casing, a fan structure, and an anti-leakage element. The casing has a top portion having an inlet, a bottom portion, and a side wall respectively connecting the top and bottom portions and having an outlet. The fan structure disposed in the casing and driven by the motor has a body connected to the motor and blades surrounding the body and being connected to the body, and rotates about an axis in a first rotation direction. The anti-leakage element extends from at least part of an edge of the inlet to an interior of the casing, partially covers parts of the blades, and extends from neighborhood of the outlet in a second rotation direction against the first rotation direction. A range of the anti-leakage element extending to the interior of the casing is gradually reduced along the second rotation direction.