A heavy duty tire comprises a tread portion provided with tread blocks each provided in the ground contact surface thereof with a single zigzag sipe. A ratio A/B of a block length (A) which is the circumferential length of the block measured along a straight line passing through the centroid of the ground contact surface to a maximum block width (B) which is the axial distance between the axial extreme ends of the ground contact surface is 0.8 to 1.7. The zigzag sipe is disposed within a central region which is defined as extending from the centroid of the ground contact surface towards each side in the tire circumferential direction by 25% of the block length (A). The zigzag sipe is composed of a pair of major straight segments extending axially inwardly from both sides of in the tire axial direction of the block, and a minor straight segment extending between the inner ends of the respective major straight segments, so that the circumferential distance between the circumferential extreme ends of the sipe is in a range of from 10 to 35% of the block length (A).