A rubber composition for use in tire side walls contains from 30 to 40 parts by mass of carbon black having a nitrogen specific surface area of from 20 to 35 m2/g and a DBP oil absorption of from 50 to 95 cm3/100 g per 100 parts by mass of a rubber component constituted by from 30 to 70 mass % of a butadiene rubber having a cis-1,4 bond content of at least 97%, a Mooney viscosity (ML1+4) at 100° C. of at least 45, and a ratio (T−cp)/(ML1+4) of the viscosity [cps] of a 5 mass % toluene solution at 25° C. (T−cp) to the Mooney viscosity of at least 2.0, and from 30 to 70 mass % of another diene-based rubber.