Disclosed is a disposable diaper having improved fittability.A disposable diaper (10) having a front waist region (11), a rear waist region (12) and a crotch region (13) located between the front and rear waist regions and includes a vertically long absorbent chassis (21) extending toward the front and rear waist regions centering on the crotch region, wherein the absorbent chassis (21) includes an absorbent structure (22) and a pair of side flaps (31) extending outward in the lateral direction from both side edges of the absorbent structure, each of the side flaps is formed of layered sheet materials and include a distal edge (32) being spaced apart in the lateral direction from the side edge of the absorbent structure and extending in the vertical direction, a cuff branch line (33) defined between the side edge of the absorbent structure and the respective distal edge so as to extend in the vertical direction, a leg-opening elasticized area (41) extending between the cuff branch line and the distal edge and leakage-barrier cuff (51) branched from the cuff branch line and extending in a direction intersecting with the leg-opening elasticized area, the leakage-barrier cuff has a free edge (52) parallelly-spaced in the lateral direction from the cuff branch line so as to extend in the vertical direction, a distance from the cuff branch line to the distal edge is larger than a distance from the cuff branch line to the free edge, and the number of sheet material layers included in the leg-opening elasticized area is larger than the number of the sheet material layers included in the leakage-barrier cuff.
