Abstract: A pneumatic radial tire for heavy vehicles comprising in combination two wide zigzag circumferential main grooves for dividing a tread into a center region and two side regions, a narrow zigzag groove for dividing each region into two portions, and a branch groove located in the center region and connected to the main and narrow grooves to define blocks and satisfying the following requirements, i.e.(1) each main groove has a width which is 5 to 9% of the width of the tread, is substantially U-shaped in cross-section and has a wall defined by a bent or wavy line whose pitch is 0.3 to 1.3 times the width of the main groove and a swing width within a range from 0.1 to 1.0 times the width of the main groove, and(2) the branch groove has a depth which is 14 to 36% of the depth of the main groove.