To provide a rubber composition for a tire capable of enhancing the grip performance while maintaining the strength, and a pneumatic tire employing the same.

Such a rubber composition for a tire is produced by blending 60 to 150 pts.mass of carbon black whose nitrogen adsorption specific surface area (N₂SA) is 120 to 400 m²/g, and 1 to 30 pts.mass of polyrotaxane compound having a cyclic molecule, a straight chain molecule enclosing the cyclic molecule in a skewer state, and closing groups disposed at both ends of the straight chain molecule preventing the cyclic molecule from being detached from the straight chain molecule, into 100 pts.mass of diene rubber comprising an aromatic vinyl-conjugated diene rubber modified by a hydroxyl group or a carboxyl group. There is also provided a pneumatic tire with cap tread in which the rubber composition for a tire is especially employed.