A centrifugal fan includes a housing and an impeller. The housing includes a base plate, a side plate extending upwardly from a periphery of the base plate and a concave portion depressed downwardly from a central portion of the base plate. The concave portion includes a bottom wall spaced from the base plate and a side wall interconnects with the base plate. An air inlet is defined in the bottom wall. The impeller includes a hub and a plurality of blades extending radially from the hub. The impeller is rotatably arranged on the bottom wall of the concave portion. A bottom face of each of the blades extends into the concave portion.