The present invention aims to provide rubber compositions and tires which provide improved overall performance in terms of wet grip performance and dry grip performance. The present invention relates to a rubber composition having a hardness that reversibly changes with water and satisfying the following relationship (1):

Hardness when dry−Hardness when water-wet≥10  (1)

wherein each hardness represents the JIS-A hardness at 25° C. of the rubber composition.