A method for manufacturing a build-up substrate, the build-up substrate comprising an insulating layer and a wiring pattern layer stacked over a circuit substrate, said method comprising the steps of: (i) applying a photoactive metal oxide precursor material to one or both sides of the circuit substrate with a wiring pattern, and drying the applied photoactive metal oxide precursor material to form an insulating film; (ii) forming an opening for a via hole in the insulating film by exposure and development of the insulating film; (iii) applying a heat treatment to the insulating film to convert the insulating film into a metal oxide film, thereby forming a build-up insulating layer of the metal oxide film; and (iv) plating the build-up insulating layer to form via holes in the openings, forming a metal layer on the build-up insulating layer, and etching the metal layer to form a build-up wiring pattern; and (v) repeating the steps from (i) to (iv) at least one time.