A rubber composition for a tire, which does not require the addition of a compound when synthesizing rubber component and the modification of a rubber component, and a studless tire using the rubber composition are provided. The rubber composition for a tire contains fine particles of rotaxane having a straight chain molecule, a cyclic molecule clathrating the straight chain molecule and blocking groups arranged at both terminals of the straight chain molecule such that the cyclic molecule does not desorb from the straight chain molecule, covered with silica; a rubber component including natural rubber and butadiene rubber; and carbon black, wherein the total content of the fine particles and the carbon black is 30 to 60 parts by mass per 100 parts by mass of the rubber component.