Abstract: An improvement of rotor disk for car disc brake includes a rotor disk and a fastening hub. The rotor disk has an opening in the center, a reinforced ring surrounding the opening and a plurality of screw bores formed in the reinforced ring. The fastening hub has a flange which has a plurality of screw bores engageable with the screw bores of the rotor disk. The flange may engage closely with the reinforced ring to increase the strength of total structure for withstanding greater stress thereby to increase stability and safety. It also may be adapted to different car modals to increase its compatibility.