A cooling fan includes: a casing having a surrounding wall that defines an accommodating space; a circuit board disposed in the accommodating space and including a substrate and a control circuit, the substrate having a center portion that has a peripheral edge, and a plurality of spaced apart connecting beams that extend from the peripheral edge of the center portion and that are connected directly and securely to the surrounding wall; a hollow shaft secured directly to and protruding from the circuit board into the accommodating space; a stator mounted securely on the center portion of the substrate of the circuit board and coupled to the control circuit; a fan blade unit disposed in the accommodating space and including an annular hub journalled rotatably to the hollow shaft; and a rotor mounted on the hub.