Abstract: A thermosetting resin composition comprising (I) a polybutadiene derivative obtained by conducting reaction of (A) a compound having active hydrogen obtained by reacting dicyclopentadiene or hydroxylated dicyclopentadiene with maleic anhydride or acid to yield partially esterified dicyclopentadienecarboxylic acid, which is further reacted with monoglycidyl ether or ester, (B) a butadiene homopolymer or copolymer having one or more hydroxyl groups and number average molecular weight of 1000 to 5000, and (C) a diisocyanate in ratios in terms of functional group equivalent ratio of (A)/(B)/(C) being 0.6-1.0/1.0/1.2-2.0, and (II) a polymerizable monomer having at least one polymerizable double bond in the molecule can be handled easily and cured at normal temperatures to give cured articles having good properties without losing excellent properties of polybutadiene as elastomer.