A polymer composition comprising (A) 100 parts by weight of a cyclo-olefinic random copolymer comprising an ethylene component and a cyclo-olefin component and having an intrinsic viscosity [.eta.] of 0.05 to 10 dl/g, a glass transition temperature (Tg) of 50.degree. to 230.degree. C., and a softening point of at least 70.degree. C., (B) 5 to 150 parts by weight of at least one flexible polymer having a glass transition temperature of not more than 0.degree. C. and (C) 0.004 to 1.0 part by weight of an organic peroxide and its reaction product.