A method for manufacturing a wiring substrate by an electroless plating method that precipitates metal without using a plating resist is provided. The method includes the steps of: (a) providing a catalyst layer having a predetermined pattern on a substrate; (b) dipping the substrate in an electroless plating solution to thereby precipitate metal on the catalyst layer to provide a first metal layer; (c) exposing a top surface of the substrate to steam; and (d) dipping the substrate in an electroless plating solution to thereby precipitate metal on the first metal layer to provide a second metal layer.