A conjugated diolefin (co)polymer rubber is provided which is small in variations in the Mooney viscosity of the resulting rubber, and in which later changes in the Mooney viscosity with the elapse of time can also be restrained. A conjugated diolefin (co)polymer rubber which is a conjugated diolefin (co)polymer rubber obtained from a conjugated diolefin or a conjugated diolefin and an aromatic vinyl compound, having an alkoxysilyl group and desolvated under alkaline conditions.