RUBBER COMPOSITION

A rubber composition obtained by kneading at least one selected from the group consisting of (A1), (B1), (C1) and (D1), a rubber component and a filler, and a method of improving the viscoelastic property of vulcanized rubber, comprising a first step of kneading at least one selected from the group consisting of (A1), (B1), (C1) and (D1), a rubber component, a filler and a sulfur component and a second step of thermally treating the kneaded material obtained in the previous step. (A1) : a compound represented by formula (I) (B1) : a salt of a compound represented by formula (I) (C1) : a solvate of a compound represented by formula (I) (D1) : a solvate of a salt of a compound represented by formula (I)