OIL-EXTENDED RUBBER AND RUBBER COMPOSITION

An oil-extended rubber comprising a conjugated diene rubber having a specific amount of isoprene units, and an extender oil incorporated therein, characterized in that the rubber is obtained by polymerizing a monomer mixture comprising 1,3-butadiene and an aromatic vinyl monomer with the aid of an organic active metal as an initiator in a hydrocarbon medium; subsequently adding isoprene to continue polymerization, then; reacting the resulting polymer having an activated terminal with a coupling agent. A rubber composition comprising the oil-extended rubber is suitable for tread of tire having a low fuel consumption.