The present technology provides a rubber composition for a tire with which it is possible to produce a tire having excellent on-ice performance and excellent wear resistance, and a studless winter tire using the rubber composition. The rubber composition for a tire of the present technology is a rubber composition for a tire comprising: 100 parts by mass of a diene rubber (A); from 30 to 100 parts by mass of carbon black and/or a white filler (B); and from 0.3 to 30 parts by mass of a cured product (C) prepared by curing a crosslinkable oligomer or polymer (c1) incompatible with the diene rubber (A); a JIS A hardness of the cured product (C) being from 3 to 45.