PURPOSE: The titled composition that is obtained by adding a halogenated ethylene.α-olefin copolymer rubber of a specific iodine value, thus improving its ozone and cold resistance without any adverse effect on its intrinsic good properties.

CONSTITUTION: (A) A nitrile rubber which is a copolymer mainly consisting of butadiene and acrylonitrile, containing 15W45wt% of acrylonitrile and having a Mooney viscosity of 20W100, and (B) a halogenated α-olefin copolymer rubber of 3W20% iodine value, preferably having halogen content of 5W35% especially 20W30% and a Mooney viscosity of 20W150, preferably 40W100, are mixed at a A/B weight ratio of 95/5W20/80, preferably 80/20W40/60. The vulcanization of the resultant composition is carried out by heating 100pts.wt. of the composition together with 5W20pts.wt. of a metal salt or 0.1W10pts.wt. of sulfur compounds or together with 3×10-4W5×10-2mol of an organic peroxide or by irradiating the composition with electron beams.