Disclosed is a heat-resistant rubber composition comprising (A) 100 parts by weight of an ethylene/a-olefin copolymer or a modified ethylene/a-olefin copolymer formed by graft-copolymerization with at least one compound selected from the group consisting of unsaturated carboxylic acids and anhydrides and esters thereof, and (B) (i) 10 to 100 parts by weight of a silica type filler which has been treated with a silane compound represented by the following formula:

wherein R' stands for an alkenyl group, a chloroalkenyl group or a chloroalkyl group, and R 2 stands for a lower alkyl group,
or (ii) a combination of 10 to 100 parts by weight of said silane-treated silica type filler or an untreated silica type filler and 0.5 to 30 parts by weight of a polyorganosiloxane having an average composition represented by the following formula:
wherein R 3 stands for a monovalent saturated or unsaturated hydrocarbon group, R 4 stands for a chloroalkyl group or an alkenyl group, a is a number of from 1 to 2.5 and b is a number of from 0.01 to 1.2, with the proviso that the sum of a and b is in the range of from 1.8 to 3.