PURPOSE: To obtain an acrylic rubber compsn. which exhibits balanced initial physical properties and a low compression set even when not subjected to postcuring by incorporating a specified amt. of an epoxidized cross-linking compd. unit into a specific acrylic rubber as the structural units and by using a specified vulcanizing agent.

CONSTITUTION: The compsn. is based on an acrylic rubber produced by copolymerizing 1.2-3.0wt.% epoxidized cross-linking compd. with the main comonomers for the rubber: ethylene, n-butyl acrylate, and vinyl acetate, and contains a combination of isocyanuric acid with a quaternary ammonium salt as the vulcanizing agent. Pref. examples of the cross-linking compd. are glycidyl acrylate and glycidyl methacrylate.