A run-flat tire having a reinforcing rubber layer having a roughly crescent-shaped meridian cross-section and being disposed in sidewall portions at both sides in a tire width direction, comprising: a tread portion being provided formed of a tread rubber that comprises a cap tread rubber (CA) and an undertread rubber (UT), the undertread rubber (UT) being disposed on an inner side of the cap tread rubber (CA) in a tire radial direction and having a higher hardness than the cap tread rubber (CA), in a meridian cross-section, a gauge (H) of the undertread rubber (UT) on a shoulder land portion on an outer side of an outermost main groove located furthest outward in the tire width direction being thicker than a gauge (H) of the undertread rubber of a center land portion closest to a tire equatorial plane (CL), wherein a gauge Ga_ce of the undertread rubber (UT) at the center land portion and a gauge Ga_sh of the undertread rubber (UT) at the shoulder land portion have a relationship Ga_ce < Ga_sh, and the gauge (H) of the undertread rubber (UT) gradually decreases from the outermost main groove toward the tire equatorial plane (CL), characterized in that the gauge (H) of the undertread rubber (UT) is determined by measuring the groove bottom of main grooves using an imaginary line (L) as a reference, and finding the average gauge within a land portion , excluding the portion of the main grooves , and a ratio W1/Wg of a width W1 in the tire width direction of a portion of the undertread rubber (UT) where the gauge (H) of the undertread rubber (UT) gradually decreases from the outermost main groove toward the tire equatorial plane (CL) to a groove width Wg of the outermost main groove is from 1.0 to 3.0. a tread portion being provided formed of a tread rubber that comprises a cap tread rubber (CA) and an undertread rubber (UT), the undertread rubber (UT) being disposed on an inner side of the cap tread rubber (CA) in a tire radial direction and having a higher hardness than the cap tread rubber (CA), in a meridian cross-section, a gauge (H) of the undertread rubber (UT) on a shoulder land portion on an outer side of an outermost main groove located furthest outward in the tire width direction being thicker than a gauge (H) of the undertread rubber of a center land portion closest to a tire equatorial plane (CL), wherein a gauge Ga_ce of the undertread rubber (UT) at the center land portion and a gauge Ga_sh of the undertread rubber (UT) at the shoulder land portion have a relationship Ga_ce < Ga_sh, and the gauge (H) of the undertread rubber (UT) gradually decreases from the outermost main groove toward the tire equatorial plane (CL), characterized in that the gauge (H) of the undertread rubber (UT) is determined by measuring the groove bottom of main grooves using an imaginary line (L) as a reference, and finding the average gauge within a land portion , excluding the portion of the main grooves , and a ratio W1/Wg of a width W1 in the tire width direction of a portion of the undertread rubber (UT) where the gauge (H) of the undertread rubber (UT) gradually decreases from the outermost main groove toward the tire equatorial plane (CL) to a groove width Wg of the outermost main groove is from 1.0 to 3.0. <EOS>