A method of manufacturing an interposer is provided, including forming a plurality of first openings on one surface side of a substrate, forming a first metal layer in the first openings, forming on the other surface side of the substrate a plurality of second openings that are in communication with the first openings, forming a second metal layer in the second openings, and electrically connecting the first metal layer to the second metal layer, so as to form conductive through holes. The conductive through holes are formed stage by stage, such that the fabrication time in forming the metal layers is reduced, and a metal material will not be accumulated too thick on a surface of the substrate. Therefore, the metal material has a smoother surface, and no overburden will be formed around end surfaces of the through holes. An interposer is also provided.