Provided is a resin composition which enables the formation of a roughened surface having a low roughness degree on the surface of an insulation layer in a printed wiring board material when used on the insulation layer regardless of the roughening conditions employed and also enables the formation of a conductive layer having excellent adhesion properties, heat resistance, heat resistance under absorption of moisture, thermal expansion properties and chemical resistance on the roughened surface. A resin composition comprising (A) an inorganic filler that is soluble in an acid, (B) a cyanic acid ester compound and (C) an epoxy resin.