A reactive injection molding resinous composition which is excellent in molding, properties and capable of resulting an injection-molded polyurea product having both excellent heat resistance and impact strength is provided, the resinous composition comprising, as polyamine components:(1) a polyoxyalkylene polyamine having an average molecular weight of 1,000-10,000 and 2 or more aliphatic amino groups,(2) a polyoxyalkylene polyamine product (A) obtained by the reaction of a polyoxyalkylene polyepoxy compound having an average molecular weight of 1,000-10,000 and an aromatic diamine having a molecular weight of 108-400,(3) a polyoxyalkylene polyamine product (B) obtained by the reaction of a polyoxyalkylene polyepoxy compound having an average molecular weight of 270-1,000 and an aromatic diamine having a molecular weight of 108-400, and(4) an aromatic diamine having at least one alkyl or thioalkyl substituent at the ortho position of respective amino group and an average molecular weight of 122-400, and as polyisocyanate components,(5) an aromatic polyisocyanate compound having an average molecular weight of 174-1,500,(6) an aliphatic polyisocyanate compound having an average molecular weight of 158-1,500, and(7) a liquid polyisocyanate prepolymer product obtained by the reaction of said (5) or (6) and a liquid polydiene compound having an average molecular weight of 1,000-5,000 and having 2 or more reactive functional groups selected from HD, amino, carboxyl and epoxy groups.