A method for fabricating an interposer is provided, which includes the steps of: providing a substrate body having a chip mounting side and an opposite external connection side and a plurality of conductive through holes communicating the chip mounting side and the external connection side, wherein the chip mounting side of the substrate body is covered with a protection layer; performing a singulation process on the external connection side of the substrate body; bonding the substrate body to a carrier via the external connection side thereof; removing the protection layer; and removing the carrier to form a plurality of interposers, thereby simplifying the fabrication process and improving the product yield.