A centrifugal fan includes a shell, an impeller, a tongue portion, and a protrusion. The shell includes a top plate, a bottom plate, and a sidewall connecting to the top plate and the bottom plate. The top plate, the bottom plate, and the sidewall define an air outlet. The impeller is disposed in the shell. The tongue portion is disposed in the shell and neighboring the air outlet. The protrusion is disposed on an inner wall of the shell and is physically connected to the top plate and the bottom plate.