Acrylic rubber composition

An acrylic rubber composition containing an acrylic ester polymer having a weight-average molecular weight of at least 8,000,000 as a rubber component, said acrylic ester polymer being a polymer obtained by emulsion polymerization of a monomer mixture mainly comprising at least one monomer selected from the group consisting of an acrylic ester represented by formula (I):

• ##STR5## wherein R.sup.1 represents an alkyl group or cyanoalkyl group having from 1 to 18 carbon atoms, and an acrylic ester represented by formula (II):
• ##STR6## wherein R.sup.2 represents an alkylene group having from 1 to 12 carbon atoms;
• and R.sup.3 represents an alkyl group having from 1 to 12 carbon atoms, said emulsion polymerization being carried out in the presence of a polymerization initiator system consisting of an oxidizing agent, a reducing agent, and an activator, with the proportion of said oxidizing agent being from 0.001 to 0.2 parts by weight per 100 parts by weight of the total acrylic ester monomers, and in the presence of a small amount of an emulsifying agent, while maintaining the dissolved oxygen concentration of the aqueous phase of the reaction system at lower than that of a 0.5% aqueous solution of sodium bisulfite, said weight-average molecular weight indicating styrene polymer conversion measured by gel-permeation chromatography, or, when said acrylic ester polymer can not be completely dissolved in a solvent for gel-permeation chromatography, the weight-average molecular weight being measured for an acrylic ester polymer obtained by replacing the monomer unit containing a functional group responsible for the insolubility, with a neutral monomer, the main constituent of said acrylic ester polymer.