Abstract: In an underpants type disposable diaper comprising a liquid permeable top sheet, a liquid impermeable back sheet, an absorbent member disposed therebetween, an elastic expansible member for forming a gather each to a pair of leg portions and front and rear waist body portions formed around the absorbent member, the front and rear waist body portions being connected and fixed together at both sides to form a waist opening portion and a pair of leg opening portions, respectively, at least a part of each area formed between the waist opening portions and the pair of leg opening portions at both side portions of the waist portion is provided with a vertical split portion, respectively and connection means are provided to each of the side portions.