A method of preparing a rubber composition for a tire comprising initiating kneading of a rubber component and a polysulfide compound represented by the following formula or before kneading the rubber component and a silane coupling agent having a mercapto group: wherein R 1 s are the same or different, and represent monovalent hydrocarbon groups which have 3 to 15 carbon atoms and may have a substituent, and n represents an integer of 2 to 6, wherein R 2 s are the same or different, and represent divalent hydrocarbon groups which have 3 to 15 carbon atoms and may have a substituent, and m represents an integer of 2 to 6, wherein the method is carried out according to procedure or below: kneading the rubber component and the polysulfide compound represented by formula or in an X-kneading step (a step X) and thereafter kneading, in a Y-kneading step (a step Y), the silane coupling agent having a mercapto group with the kneaded product obtained in the step X, or, alternatively, in the step X, the rubber component and the polysulfide compound represented by formula or are kneaded for a given period of time (a step X1), and thereafter, without discharging the kneaded product, the silane coupling agent having a mercapto group is added, followed by further kneading, wherein, in the step X, silica is further kneaded and the silica is added earlier than the addition of the silane coupling agent having a mercapto group; a kneaded product X is obtained by kneading the rubber component and the polysulfide compound represented by formula or (step X1); adding and kneading reinforcing agents such as carbon black and silica (step X2); and further adding and kneading the silane coupling agent having a mercapto group (step X3), followed by discharging; thereafter silica and the silane coupling agent having a mercapto group are added to the kneaded product X, followed by kneading (step Y) and then discharging to obtain a kneaded product Y; next, silica and the silane coupling agent having a mercapto group are added to the kneaded product Y, followed by kneading (step Z) and then discharging to obtain a kneaded product Z; and then an unvulcanized rubber composition is obtained by adding the vulcanizing agent and the vulcanization accelerator to the obtained kneaded product Z and subjecting the mixture to kneading (step F). kneading the rubber component and the polysulfide compound represented by formula or in an X-kneading step (a step X) and thereafter kneading, in a Y-kneading step (a step Y), the silane coupling agent having a mercapto group with the kneaded product obtained in the step X, or, alternatively, in the step X, the rubber component and the polysulfide compound represented by formula or are kneaded for a given period of time (a step X1), and thereafter, without discharging the kneaded product, the silane coupling agent having a mercapto group is added, followed by further kneading, wherein, in the step X, silica is further kneaded and the silica is added earlier than the addition of the silane coupling agent having a mercapto group; a kneaded product X is obtained by kneading the rubber component and the polysulfide compound represented by formula or (step X1); adding and kneading reinforcing agents such as carbon black and silica (step X2); and further adding and kneading the silane coupling agent having a mercapto group (step X3), followed by discharging; thereafter silica and the silane coupling agent having a mercapto group are added to the kneaded product X, followed by kneading (step Y) and then discharging to obtain a kneaded product Y; next, silica and the silane coupling agent having a mercapto group are added to the kneaded product Y, followed by kneading (step Z) and then discharging to obtain a kneaded product Z; and then an unvulcanized rubber composition is obtained by adding the vulcanizing agent and the vulcanization accelerator to the obtained kneaded product Z and subjecting the mixture to kneading (step F).