The present invention provides a flip-chip package substrate and a method for fabricating a flip-chip package substrate comprising a circuit build-up structure, which comprises at least a dielectric layer and at least a circuit layer, wherein each dielectric layer comprises a first surface and a second surface, plural vias are formed in the first surface, the circuit layer is formed on the first surface and in the vias to electrically connect to another circuit layer disposed under the dielectric layer; a metal layer embedded in the exposed second surface of the circuit build-up structure without protruding the exposed second surface and connected to the circuit layer; and two solder masks disposed on the exposed first surface and the exposed second surface of the circuit build-up structure, wherein the solder masks have plural openings to separately expose part of the circuit layer and the metal layer functioning as conductive pads.