Provided are: a rubber composition for studless winter tires, achieving balanced improvement in performance on ice and snow, wet grip performance, and abrasion resistance; and a studless winter tire including a tread formed from the same. The rubber composition for studless winter tires includes: a rubber component including NR and BR; an aromatic oil; silica; and carbon black, wherein the combined amount of NR and BR is 30 mass % or more per 100 mass % of the rubber component; the amount of aromatic oil is 12-85 parts by mass per 100 parts by mass of the rubber component; the silica content is 45 mass % or more per 100 mass % in total of silica and carbon black; the silica includes at least one silica (1) with an N2SA of 100 m2/g or less and at least one silica (2) with an N2SA of 180 m2/g or more; the combined amount of silicas (1) and (2) is 30-150 parts by mass per 100 parts by mass of the rubber component; and the amounts of silicas (1) and (2) satisfy: [Amount of silica (1)]×0.2≦[Amount of silica (2)]≦[Amount of silica (1)]×6.5.