There are provided a resin composition comprising a crosslinking component with a weight average molecular weight of 1,000 or less having a plurality of styrene groups and represented by the following formula: wherein R is a hydrocarbon skeleton, each of R1s is a hydrogen atom or a hydrocarbon group, each of R2, R3 and R4 is a hydrogen atom or an alkyl group, m is an integer of 1 to 4, and n is an integer of 2 or more, at least one high-molecular weight compound, an inorganic filler, and at least one treating agent for said inorganic filler; its cured product; and a prepreg, a laminate sheet having a conductor layer, and a multilayer printed wiring board obtained by processing the conductor layer of the laminate sheet into wiring.