In a substrate of a printed circuit, a metal foil is mounted onto at least one of the outermost surfaces of a laminate made of a plurality of glass fiber woven fabrics impregnated with synthetic resin, and heated and pressed. Warps and wefts of the glass fiber fabrics filamentated their filaments. The synthetic resin enters gaps among the opening filaments so that the vertically laminated glass fiber fabrics including the opening fibers are integrally jointed with each other. Warps and wefts of the glass fiber fabrics may have their surfaces made fuzzy so that the synthetic resin enters fuzzy filaments. Furthermore, the thus produced substrate may be used as a multilayer printed circuit substrate.