Rubber composition

A vulcanizable rubber composition comprising a copolymer rubber constituted of ethylene, propylene and 5-ethylidene-2-norbornene and/or dicyclopentadiene, wherein ethylene/propylene molar ratio is 86/14 to 97/3, the total content of propylene and 5-ethylidene-2-norbornene and/or dicyclopentadiene is 6 to 30% by mole, the content of 5-ethylidene-2norbornene and/or dicyclopentadiene is 3 to 6% by mole, wherein the ratio of the contents of the ingredients (A) is defined by the following equation:

• ##EQU4## wherein each of P, D and E represents the content (% by mole) of propylene, 5-ethylidene-2-norbornene and/or dicyclopentadiene and ethylene, respectively, in the copolymer of A.gtoreq.0.1, and said copolymer rubber has an intrinsic viscosity of 0.8 to 4.0 dl/g as measured at 70.degree. C. in xylene, a melting peak temperature of 70.degree. C. or below and a heat quantity of melting of 10 cal/g or below as measured with a differential scanning calorimeter and a process oil in an amount of 10 to 150 parts by weight per 100 parts by weight of the copolymer rubber.