A pneumatic tire has a unidirectional tread pattern. On each side of the tire equator, there are a circumferential groove and main oblique grooves extending form the tread edge to the circumferential groove while inclining to the intended tire rotational direction and gradually decreasing its inclination angle with respect to the tire circumferential direction. The inclination angle of the main oblique groove measured at the tread edge is 60 to 120 degrees. The width of the main oblique groove is gradually increased toward the axially outside from the circumferential groove. The width of the circumferential groove becomes narrower at heel-side ends of shoulder blocks than at toe-side ends of the shoulder blocks. The shoulder block is provided with an auxiliary oblique groove extending from the main oblique groove toward the intended tire rotational direction and terminating without reaching to the next main oblique groove.