Process for producing conjugated diene rubber and composition of the same conjugated diene rubber are presented. The process includes polymerizing a conjugated diene or a conjugated diene and a vinyl aromatic hydrocarbon in a hydrocarbon solution by anionic polymerization using an organic alkali metal compound to obtain conjugated diene rubber containing alkali metal in the polymer chain end reacting a conjugated diene rubber containing alkali metal in the polymer chain end with at least one organic silane compound to obtain a modified conjugated diene rubber. After or during the modified conjugated diene rubber contacting with large amount of water, solvent and water content are removed from the modified conjugated diene rubber by applicable hot sources, wherein coupling ratio of modified conjugated diene rubber is less than 40 %, coupling ratio of modified conjugated diene rubber after contact with water is at least 50 %, and difference of Mooney viscosity (MV) between initial MVi (after water treatment) and MVs (after storage test in 90 °C, 80 % relative humidity and 40 hours) is less than or equal to 10, and a mixture of silica compound and conjugated diene rubber.