A rubber composition comprising 0.1 to 2.5 parts by weight of a lubricant having a flow temperature of 50 to 100° C. based on 100 parts by weight of an ethylene/butene/5-ethylidene-2-norbornene terpolymer. This rubber composition is compounded with a specific lubricant, has the following effects. That is, the rubber composition prevents difficulties caused by sticking between unvulcanized rubber compound, improves productivity in the rubber compound preparation process and the vulcanization molding process of crosslinked molded products, such as seal members, and does not impair the low temperature properties of the crosslinked molded products. This rubber composition is effectively used as a crosslinking molding material for seal parts, for which a high pressure gas sealing function is particularly required in a low temperature environment, e.g., −39° C. or lower.