An oil extended rubber comprising 100 parts by weight of (A) an amino group-containing copolymer rubber of a conjugated diolefin and an aromatic vinyl compound which contains bonded amino groups in the amount of 0.0025-0.20 mmol/g polymer, and 10-100 parts by weight of (B) an extensible oil. Carbon black, silica, a mixture of carbon black and silica, or a carbon-silica dual-phase-filler can be homogeneously dispersed in the oil extended rubber. Vulcanized products obtained by vulcanizing the rubber exhibits well-balanced improved properties such as wet skid properties, low hysteresis loss properties, abrasion resistance, and breaking strength, and are useful as a tread material for low fuel consumption tires, large tires, and high performance tires.