A pneumatic tire has improved run-flat endurance, driving stability, and ride quality, which are achieved without increasing rolling resistance. Provided is a pneumatic tire configured so that: the direction of mounting of the tire on a vehicle relative to the inside and outside of the vehicle is specified; and reinforcement rubber layers having a substantially crescent-shaped meridional cross-section are arranged in sidewalls on both sides of the tire in the width direction thereof. In a non-loaded state of the tire, in which the tire is mounted to a regular rim and pressure within the tire is set to 0 kPa, the following straight lines are drawn: a straight line perpendicular to the equatorial plane of the tire drawn at the maximum tire width section of a meridional cross-section of the tire; a straight line extending from the point of intersection of said straight line with the equatorial plane of the tire and tilted 10o toward the outside in the radial direction of the tire relativeto said straight line; and a straight line tilted 10o toward the inside in the radial direction of the tire. Then the relationship between the curvature radius of the circular arc connecting the points of intersection between the outline of the tire and the straight lines, and the curvature radius of the circular arc connecting the points of intersection between the carcass layer and the straightlines causes that, on the side of the tire which faces the outside of the vehicle, the curvature radius of the carcass layer is large relative to that of the outline of tire, and causes also that, onthe side of the tire which faces the inside of the vehicle, the curvature radius of the carcass layer is small relative to that of the outline of tire.