A centrifugal blower (10) includes a casing (12) and a rotor (14) rotatable disposed in the casing. The casing includes a base plate (121), a sidewall (122) extending from the base plate and a cover (123) covering the sidewall. The sidewall is a multilayer structure and includes a first section (128a) and a second section (128c). A distance between a central axis (A) of the rotor and an inner surface of the second section is greater than that between the central axis of the rotor and an inner surface of the first section. The first section is located below a mother board (20) and the second section sits on a top surface of the motherboard when the centrifugal blower is mounted to the mother board.