A single-layer wiring package substrate and a method of fabricating the same are provided, the method including: forming on a carrier a wiring layer having a first surface and a second surface opposing the first surface and being in contact with the carrier; forming on the carrier and on the wiring layer a dielectric body that has a first side having a first opening, from which a portion of the wiring layer is exposed, and a second side opposing the first side and disposed at the same side as the second surface of the wiring layer; and removing the carrier, with the second side of the dielectric body and the second surface of the wiring layer exposed. Therefore, a coreless package substrate is fabricated, and the overall thickness and cost of the substrate are reduced.