A pneumatic tire comprising: a tread portion being provided with a shoulder block row comprising a plurality of circumferentially arranged shoulder blocks on at least one side of tread edges (Te); the shoulder blocks comprising a first shoulder block and a second shoulder block alternately arranged in a circumferential direction of the tire ; the first shoulder block comprising a first edge defining an axially outermost ground contact edge of its ground contact surface ; and the second shoulder block comprising a second edge defining an axially outermost ground contact edge of its ground contact surface , the second edge being located axially inwardly of the first edge ; wherein the tire further comprises a buttress surface which is a radially outward region of a sidewall portion (Sw), in a tire meridian cross-sectional view including a tire rotational axis under a standard condition such that the tire is mounted on a standard wheel rim with a standard pressure, but is loaded with no tire load, the buttress surface is provided with a plurality of circumferentially arranged projections protruding axially outwardly, the projections comprise a first projection having a circumferential width decreasing smoothly toward radially inwardly, the second shoulder block comprises a side surface extending radially inwardly and axially outwardly from the second edge , and the first projection is connected to the second edge through the side surface of the second shoulder block , characterized in that the projections further comprise a second projection having a circumferential width increasing smoothly toward radially inwardly, and the first projection and the second projection are arranged alternately in the circumferential direction of the tire . a tread portion being provided with a shoulder block row comprising a plurality of circumferentially arranged shoulder blocks on at least one side of tread edges (Te); the shoulder blocks comprising a first shoulder block and a second shoulder block alternately arranged in a circumferential direction of the tire ; the first shoulder block comprising a first edge defining an axially outermost ground contact edge of its ground contact surface ; and the second shoulder block comprising a second edge defining an axially outermost ground contact edge of its ground contact surface , the second edge being located axially inwardly of the first edge ; wherein the tire further comprises a buttress surface which is a radially outward region of a sidewall portion (Sw), in a tire meridian cross-sectional view including a tire rotational axis under a standard condition such that the tire is mounted on a standard wheel rim with a standard pressure, but is loaded with no tire load, the buttress surface is provided with a plurality of circumferentially arranged projections protruding axially outwardly, the projections comprise a first projection having a circumferential width decreasing smoothly toward radially inwardly, the second shoulder block comprises a side surface extending radially inwardly and axially outwardly from the second edge , and the first projection is connected to the second edge through the side surface of the second shoulder block , characterized in that the projections further comprise a second projection having a circumferential width increasing smoothly toward radially inwardly, and the first projection and the second projection are arranged alternately in the circumferential direction of the tire . <EOS>