A process for preparing a vulcanized rubber composition comprising: (a) a step of preparing a master batch comprising a modified conjugated diene polymer and silica, (b) a step of preparing a master batch comprising an isoprene rubber and silica, (c) a step of kneading the master batch obtained in the step (a) and the master batch obtained in the step (b), and (d) a step of vulcanizing a kneaded product obtained in the step (c), wherein the vulcanized rubber composition comprises: a phase comprising the modified conjugated diene polymer and silica (phase A), and a phase comprising the isoprene rubber and silica (phase B), wherein the phase A and the phase B are incompatible with each other, wherein "incompatible" means that an averaged equivalent circle radius of a discontinuous phase in the section of the vulcanized rubber composition is 100 nm or more, when evaluated by an image taken with a scanning electron microscope, an abundance ratio α of silica in the phase A 100 to 500 hours after completion of a vulcanization step satisfies the following Relation 1, and a proportion β of the modified conjugated diene polymer satisfies the following Relation 2: 0.5 ≤ α ≤ 0.9 0.4 ≤ β ≤ 0.8 wherein α = Amount of silica in phase A / Amount of silica in phase A + Amount of silica in phase B and β = Mass of modified conjugated diene polymer in vulcanized rubber composition / Mass of modified conjugated diene polymer in vulcanized rubber composition + Mass of isoprene rubber in vulcanized rubber composition, wherein the master batch comprising the modified conjugated diene polymer and silica comprises not less than 40 parts by mass of silica based on 100 parts by mass of the modified conjugated diene polymer, and wherein the master batch comprising the isoprene rubber and silica comprises not less than 15 parts by mass of silica based on 100 parts by mass of the isoprene rubber. (a) a step of preparing a master batch comprising a modified conjugated diene polymer and silica, (b) a step of preparing a master batch comprising an isoprene rubber and silica, (c) a step of kneading the master batch obtained in the step (a) and the master batch obtained in the step (b), and (d) a step of vulcanizing a kneaded product obtained in the step (c), wherein the vulcanized rubber composition comprises: a phase comprising the modified conjugated diene polymer and silica (phase A), and a phase comprising the isoprene rubber and silica (phase B), wherein the phase A and the phase B are incompatible with each other, wherein "incompatible" means that an averaged equivalent circle radius of a discontinuous phase in the section of the vulcanized rubber composition is 100 nm or more, when evaluated by an image taken with a scanning electron microscope, an abundance ratio α of silica in the phase A 100 to 500 hours after completion of a vulcanization step satisfies the following Relation 1, and a proportion β of the modified conjugated diene polymer satisfies the following Relation 2: 0.5 ≤ α ≤ 0.9 0.4 ≤ β ≤ 0.8 wherein α = Amount of silica in phase A / Amount of silica in phase A + Amount of silica in phase B and β = Mass of modified conjugated diene polymer in vulcanized rubber composition / Mass of modified conjugated diene polymer in vulcanized rubber composition + Mass of isoprene rubber in vulcanized rubber composition, wherein the master batch comprising the modified conjugated diene polymer and silica comprises not less than 40 parts by mass of silica based on 100 parts by mass of the modified conjugated diene polymer, and wherein the master batch comprising the isoprene rubber and silica comprises not less than 15 parts by mass of silica based on 100 parts by mass of the isoprene rubber. a phase comprising the modified conjugated diene polymer and silica (phase A), and a phase comprising the isoprene rubber and silica (phase B), wherein the phase A and the phase B are incompatible with each other, wherein "incompatible" means that an averaged equivalent circle radius of a discontinuous phase in the section of the vulcanized rubber composition is 100 nm or more, when evaluated by an image taken with a scanning electron microscope, an abundance ratio α of silica in the phase A 100 to 500 hours after completion of a vulcanization step satisfies the following Relation 1, and a proportion β of the modified conjugated diene polymer satisfies the following Relation 2: 0.5 ≤ α ≤ 0.9 0.4 ≤ β ≤ 0.8 wherein α = Amount of silica in phase A / Amount of silica in phase A + Amount of silica in phase B and β = Mass of modified conjugated diene polymer in vulcanized rubber composition / Mass of modified conjugated diene polymer in vulcanized rubber composition + Mass of isoprene rubber in vulcanized rubber composition, wherein the master batch comprising the modified conjugated diene polymer and silica comprises not less than 40 parts by mass of silica based on 100 parts by mass of the modified conjugated diene polymer, and wherein the master batch comprising the isoprene rubber and silica comprises not less than 15 parts by mass of silica based on 100 parts by mass of the isoprene rubber.