To provide an underpants type absorbent article capable of achieving excellent fitting property in a crotch part and a hip part of an absorbent core.SOLUTION: An underpants type absorbent article (1) has an absorbent body (10) which comprises an absorbent core (11) disposed along a vertical direction and is folded from front to rear at a lower end in the vertical direction. The absorbent core (11) has a rear side part (10R) which is a portion folded to the rear side in a longitudinal direction. The absorbent core (11) has a rear side low basis weight region (39) having a lower average basis weight than that of a surrounding region in the rear side part (10R), and a hip part high basis weight region (55) provided above the rear side low basis weight region (39) in the vertical direction and having a higher average basis weight than that of the rear side low basis weight region (39). At least a part of a boundary (55BF) between the rear side low basis weight region (39) and the hip part high basis weight region (55) is inclined obliquely downward from the center in a right direction toward both outer sides.SELECTED DRAWING: Figure 6【課題】吸収性コアの股間部及び臀部において良好なフィット性を実現可能なパンツ型吸収性物品を提供する。【解決手段】上下方向に沿って配置された吸収性コア（１１）を備え、上下方向の下端部にて前後に折り曲げられた吸収性本体（１０）、を有するパンツ型吸収性物品（１）であって、吸収性コア（１１）は、前後方向の後側に折り曲げられた部分である後側部（１０Ｒ）を有し、吸収性コア（１１）は、後側部（１０Ｒ）において、周囲の領域よりも平均坪量が低くなっている後側低坪量領域（３９）と、後側低坪量領域（３９）よりも上下方向の上側に設けられ、後側低坪量領域（３９）よりも平均坪量が高くなっている臀部高坪量領域（５５）と、を有し、後側低坪量領域（３９）と臀部高坪量領域（５５）との境界部（５５ＢＦ）の少なくとも一部は、前記右方向の中央から両外側に向けて斜め下方向に傾斜している。【選択図】図６
