A pneumatic radial tire comprises (1) a pair of left and right bead portions, (2) a pair of left and right side-wall portions continuing from the respective bead portions, (3) a tread portion positioned between the side-wall portions, (4) a carcass layer provided between the left and right bead portions a cord angle of which is substantially 90 degree in relation to the circumferential direction of the tire, (5) an auxiliary carcass layer a cord angle of which is substantially 0 degree in relation to the circumferential direction of the tire, being placed on the tread side of the carcass layer substantially to correspond to the tread portion, so that the carcass layer and the auxiliary carcass layer may be crossed substantially at a right angle to form a net structure, and (6) a belt reinforcement layer having a tensile ridigity, at the circumferential of the tire, of not less than 10 kg/mm2, being placed on the auxiliary carcass layer substantially to correspond to the tread portion.