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 a crosslinking monomer.