A rubber composition comprising (a) a low molecular weight copolymer rubber which is an ethylene/null-olefin/non-conjugated diene copolymer rubber having a limiting viscosity nullnullnull of 0.4-1.6 dl/g measured in decalin at 135null C., and an ethylene content of 40-60 wt % and (b) a high molecular weight copolymer rubber which is an ethylene/null-olefin/non-conjugated diene copolymer rubber having a Mooney viscosity (ML1null4,100null C.) of 60-150, an ethylene content of 60-80 wt %, and an iodine number of 5-35, wherein the difference between the iodine number of the low molecular weight copolymer rubber (a) and the iodine number of the high molecular weight copolymer rubber (b) is 5 or less and the ratio by weight of the low molecular weight copolymer rubber (a) and the high molecular weight copolymer rubber (b) is 50/50 to 80/20, the rubber composition having a Mooney viscosity (ML1null4,100null C.) of 20-50. The rubber composition exhibits superior roll processability and extrusion processability, excellent surface appearance and adhesiveness, can be processed easily, and produces vulcanized rubber exhibiting excellent mechanical characteristics and good low and high temperature properties.