There is provided a rubber composition for a side wall, wherein an amount ratio of resources other than petroleum are increased so as to be ecological and take measures for the decrease in supply of petroleum in the future, which further has excellent flex crack resistance and strength.A rubber composition for a side wall comprising 20 to 60 parts by weight of silica based on 100 parts by weight of a rubber component comprising 40 to 80% by weight of a natural rubber and 60 to 20% by weight of at least one rubber selected from the group consisting of a butadiene rubber, a styrene-butadiene rubber and an epoxidized natural rubber, and 4 to 16 parts by weight of a silane compound represented by the following formula: X.sub.n--Si--Y.sub.4-n (wherein X represents an ethoxy group or a methoxy group, and Y represents a phenyl group or an alkyl group) based on 100 parts by weight of silica.