A rubber composition controlling the increase of aging hardness of a studless tire and keeping good performance on snow and ice for long period is provided. A rubber composition for a studless tire including at most 0.5 part by weight of sulfur and 1 to 30 parts by weight of an organic vulcanizing agent satisfying the general formula (1): —(R—Sx)n—  (1) (wherein R is (CH2—CH2—O)m—CH2—CH2, x is an integer of 3 to 6, n is an integer of 10 to 400 and m represents an integer of 2 to 5) based on 100 parts by weight of a rubber component, wherein the content of a natural rubber and/or a polybutadiene rubber is at least 80% by weight in the rubber component, and tan δ peak temperature Tg is at most −50° C. and rubber hardness at 0° C. is at most 64.