The present invention provides a tread rubber composition for a studless tire having favorable performance on ice and snow and excellent abrasion resistance while reducing strain dependence of hardness of the tread rubber and maintaining rigidity on roads that are not covered with snow and relates to a tread rubber composition for a studless tire, which comprises a diene rubber containing, in a total amount of 80% by mass or more, natural rubber and polybutadiene rubber; silica in an amount of 10 to 150 parts by mass per 100 parts by mass of the diene rubber; and carbon black in an amount of 3 to 50 parts by mass per 100 parts by mass of the diene rubber, wherein the diene rubber contains 10% by mass or more of a polybutadiene rubber modified by a compound represented by the formula (I): R1, R2 and R3 being independently an alkyl group, analkoxy group, a silyloxy group, an acetal group, a carboxyl group, a mercapto group, or a derivative thereof; R4 and R5 being independently a hydrogen atom or an alkyl group; and n being an integer.