An ethylene-.alpha.-olefin-non-conjugated diene copolymer rubber composition which comprises two kinds of ethylene-.alpha.-olefin-non-conjugated diene copolymers, �the copolymers (A) and (B)!, copolymer (A) containing ethylidenenorbornene and either dicyclopentadiene or .alpha.,.omega.-diene having 8 to 20 carbon atoms in the main chain as the non-conjugated dienes, copolymer (B) containing ethylidenenorbornene as the non-conjugated diene, the weight ratio of the copolymer (A) to the copolymer (B) being 30/70 to 70/30, wherein the copolymer (A) has a relatively low molecular weight, a specific ethylene/.alpha.-olefin weight ratio and a specific non-conjugated diene content and the copolymer (B) has a relatively high molecular weight and a specific ethylene/.alpha.-olefin weight ratio. Said copolymer rubber composition, when highly foamed, shows no reduction particularly in low tensile stress, and is excellent in shape-retention during cross-linking and foaming, and in compression set and processibility.