An apparatus for assembling a lens module, is provided. The lens module includes a lens and a lens holder for receiving the lens. The lens holder has a through hole and a retainer formed in the through hole. The apparatus includes a base for supporting the lens holder, and a supporter formed on the base, for extending through the through hole of the lens holder and supporting the lens thereon. A height of the supporter is greater than a depth of the through hole of the lens holder. The supporter is movable relative to and away from the lens holder so as to place the lens on the retainer in the through hole of the base.