PURPOSE: To obtain a rubber composition of high adhesivity to steel cords, with good processability in uncured state, capable of providing cured rubber with high rigidity and rupture resistance, comprising a raw rubber containing a specific amount of natural rubber, and each specific amount of a rosin cobalt salt, carbon black, and sulfur.

CONSTITUTION: The objective rubber composition comprising (A) 100 parts by wt. of a raw rubber containing ≥80wt% of natural and/or synthetic polyisoprene rubber, (B) 0.02W0.8 (pref. 0.05W0.4) parts by wt., in terms of cobalt elements, of a rosin cobalt salt, (C) 60W100 parts by wt. of carbon black with an iodine adsorption 70W130mg/g and a DBP oil absorption 50W80ml/100g, (D) 4.5W10 parts by wt. of sulfur, and, if required, (E) zinc oxide, process oil, curing accelerator.

USE: For vehicle tires, etc.