To obtain the subject composition, further improved in strength characteristics and abrasion resistance and useful as a rubber material such as a belt by compounding a metallic salt of an α,β-methacrylic acid and an organic peroxide oxide therewith.

This composition is obtained by compounding (A) a carboxylated nitrile group-containing highly saturated copolymer rubber having ≥2×10-3 ephr acid equive., 15-200 Mooney viscosity and ≤80 iodine value with (B) a metallic salt of an α,β-ethylenically unsaturated carboxylic acid (e.g. zinc methacrylate) and (C) an organic peroxide (e.g. dicumyl peroxide). Furthermore, e.g. a metallic salt having a structure in which a ≤5C ethylenically unsaturated carboxylic acid having one or two or more carboxyl groups (concretely acrylic acid, etc.) and a metal such as zinc are bonded through an ionic bond is preferably used as the component B.