Resin compositions, which contain: (a) a heat-resistant resin which is soluble in organic solvents wherein the heat-resistant resin is one or more heat-resistant resin(s) selected from the group consisting of a polyimide resin, a polyamide-imide resin, a polyamide resin, a polyether imide resin, a polybenzoxazol resin, a polybenzimidazole resin, copolymers thereof, and mixtures thereof; (b) a thermosetting resin; (c) a filler; and (d) resin having a polybutadiene structure and/or a polysiloxane structure, wherein: the heat-resistant resin (a) and the thermosetting resin (b) are present in a weight ratio of heat-resistant resin (a) to thermosetting resin (b) of from 100:1 to 1:1; the heat-resistant resin (a), thermosetting resin (b), and filler (c) are present in relative amounts such that weight ratio of the total amount of heat-resistant resin (a) and thermosetting resin (b) to filler (c) by weight is from 100:1 to 3:2; the resin having a polybutadiene structure and/or a polysiloxane structure (d) is present in an amount of 0.1 to 15 parts by weight based on 100 parts by weight of the heat-resistant resin (a); and the heat-resistant resin (a), thermosetting resin (b), filler (c), and resin having a polybutadiene structure and/or a polysiloxane structure (d) are present in a total amount of not less than 70% by weight, based on the total weight of the resin composition, are useful for preparing adhesive films, which are, in turn, useful for forming interlayer insulation layers for multi-layered printed wiring boards having an excellent mechanical strength and capable of being roughened by an oxidizing agent.