Provided by the present invention are a rubber composition for studless winter tires capable of improving performance on snow and ice while maintaining good abrasion resistance, and a studless winter tire including the rubber composition. The present invention relates to a rubber composition for studless winter tires containing a rubber component and bionanofibers, the bionanofibers having an average fiber diameter of 0.1 μm or less, the rubber component having a combined amount of natural rubber and polybutadiene rubber of 30% to 100% by mass based on 100% by mass of the rubber component, the rubber composition containing the bionanofibers in an amount of 1 to 10 parts by mass relative to 100 parts by mass of the rubber component.