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.