To provide a new rubber composition suitable for tread of a pneumatic tire, excellent in characteristics of frictional resistance and tear resistance.

This sulfur-vulcanizable rubber composition comprises a chlorosulfonated polyethylene in an amount of about 1.0-15 pts.wt. based on 100 pts.wt. of the amount of the total rubber contained in the composition, a carboxylated nitrile rubber in an amount of about 1.0-15 pts.wt., and a rubber selected from a group comprising polybutadiene with a medium vinyl content, styrene-butadiene rubber, synthesized cis-1,4-polyisoprene, synthesized cis-3,4- polyisoprene, natural rubber, cis-1,4-polybutadiene, styrene-isoprene rubber, styrene-isoprene-butadiene rubber, acrylonitrile-butadiene rubber and their mixtures in an amount of 98-70 pts.wt. The rubber composition is especially suitably used for the tread of the tire.