Abstract: A thermoplastic elastomer with well-balanced physical properties is prepared by treating a rubber/resin composition comprised of (a) 45-90 wt. parts of a rubbery component and (b) 10-55 wt. parts of a polyolefin resin, with a curing agent. The rubbery component (a) is comprised of 5-100 wt. % of an ethylene-propylene copolymer rubber having an ethylene content of 60-78 mole %, a crystallinity of 4 to 20%, a maximum peak temperature of melting of at least 100.degree. C., an MFI of less than 0.01 at 230.degree. C., an HLMFI/MFI of at least 35, an Mw/Mn of at least 4, and a tensile strength at break of at least 100 kg/cm.sup.2, and 95-0% by weight of an ethylene-propylene-nonconjugated diene copolymer. The rubbery component in the cured product has a gel content more than 80 wt. % and less than 97 wt. % as determined by immersion in cyclohexane at 23.degree. C. for 48 hours.