A radiation-sensitive resin composition comprising: (A) a phenol resin, (B) an amino resin, (C) a compound having two or more crosslinking groups in a molecule, and (D) a halomethyl-1,3,5-triazine compound. The composition can form insulating layers exhibiting high resolution, high plating solution resistance, high adhesion to conductor wiring, and developability using an alkaline aqueous solution, producing cured insulating layers with superior solvent resistance, excellent waterproofing characteristics, and high heat resistance. The composition is useful for fabricating multilayered wiring boards.