A conjugated diene rubber gel comprising 80 - 99 weight % of conjugated diene monomer units and 20 - 1 weight % of aromatic vinyl monomer units and having a swelling index of 16 to 70 as measured in toluene. A rubber vulcanizate made from a rubber composition comprising this conjugated diene rubber gel and a rubber capable of being crosslinked with sulfur exhibits good abrasion resistance and low heat-build up without deterioration of mechanical properties, and thus, is suitable for tire materials. This conjugated diene rubber gel can be produced with high efficiency by emulsion-polymerization of a monomer mixture comprising 50 - 99.9 weight % of a conjugated diene monomer, 0 - 30 weight % of an aromatic vinyl monomer, 0 - 20 weight % of other ethylenically unsaturated monomer and 0.1 - 20 weight % of a crosslinking monomer
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