A rubber composition which prevents the rise in rubber hardness over time and can maintain good performance on snow and ice over a long period, which includes (A) a diene rubber containing, as a main component, at least one member selected from the group consisting of natural rubber and butadiene rubber, and (B) 5 to 60 parts by weight of vegetable oil which has an iodine value of at least 80 and contains at least 70% by weight of unsaturated fatty acid having at least 18 carbon atoms, based on 100 parts by weight of the diene rubber (A), the rubber composition having a tan .delta. peak temperature Tg of at most -50.degree. C. and a rubber hardness of at most 64 at 0.degree. C. The present invention also relates to a pneumatic tire using the rubber composition as the tread.