A pull-on absorbent article comprising a front outer cover adapted to be worn around a wearer's front side, a rear outer cover adapted to be worn around the wearer's rear side, and an absorbent assembly fixed to the front and the rear outer covers (2A, 2B) so as to bridge them and have an overlap with them, the article, being in a flat-out, uncontracted state, having an article longitudinal direction and an article lateral direction perpendicular to the article longitudinal direction, and the article having a pair of side seals formed by joining the front outer cover and the rear outer cover along their lateral side edges (2a, 2b), each of the front and the rear outer cover (2A, 2B) having a laterally uniform length (La, Lb) in the article longitudinal direction, said length (La, Lb) being longer than side seals, and each of the front and the rear outer cover (2A, 2B) having an extension portion (21a, 21b) extending downward from the side seals, the extension portion of the front outer cover and/or the extension portion of the rear outer cover having an elasticized extension region exhibiting extensibility and contractibility in the article lateral direction in at least a region located laterally outward of each side edge of the absorbent assembly, the front and the rear outer covers (2A, 2B) of the article each include an outer sheet that defines the exterior of the article, an inner sheet laid on the inner side of the outer sheet, and a plurality of elastic members of thread form arranged between the two sheets (22, 23), the front and the rear outer covers (2A, 2B) each include an elasticized waist region, an elasticized below-waist region and the elasticized extension region, the elasticized below-waist region being located between the elasticized waist region and the elasticized extension region with respect to the article longitudinal direction, the outer and the inner sheets (22, 23) are bonded to each other at discretely arranged bonds in the elasticized waist region, the elasticized below-waist region, and the elasticized extension region, a plurality of lateral bonding lines are disposed with respect to the article lateral direction, each line consisting of the bonds 26 that are spaced with respect to the article longitudinal direction, a plurality of elastic members are arranged to pass between bonds adjacent in the article longitudinal direction in each of the elasticized regions (G1 to G3), the elasticized below-waist region and the elasticized extension region each have, along the lateral side edge of each of the front and the rear outer covers (2A, 2B), an end fixing part where the outer sheet and the inner sheet are bonded with an adhesive and an absorbent assembly-side fixing part near the side edge of the absorbent assembly where the outer sheet and the inner sheet are bonded with an adhesive, each of the elastic members disposed in the elasticized below-waist region and the elasticized extension region is secured between the sheets (22, 23) at the end fixing part and at the absorbent assembly-side fixing part, while not being fixed to either the outer sheet or the inner sheet between the end fixing part and the absorbent assembly-side fixing part, the absorbent assembly is bonded in the vicinity of its longitudinal end to the front outer cover over its whole width, the region of the absorbent assembly that overlaps the extension portion of the front outer cover has a fixed middle portion located between the opposite absorbent assembly-side fixing parts, and the region of the absorbent assembly that overlaps the extension portion also has a non-fixed side portion located outward of each side edge of the fixed middle portion.