To provide a disposable diaper for pets that fits well around the waist of the pet. A disposable diaper for pets, in which a fixed section in an attachment section overlaps with an expanding/contracting elastic member for the waist, said disposable diaper for pets having: a rear-side waist area (130) a stomach-side waist area (110) a crotch area (120) both end sections (130A, 110A) in the diaper longitudinal direction both end sections (120A) in the diaper longitude-intersecting direction a tail insertion opening (190) an absorbent core (200) an area (170) not having the absorbent core arranged therein a flap section (150) provided in the stomach-side waist area and having an end section in the rear-side direction an attachment section (300) having the fixed section (320) arranged in the flap section (150) and a free section (310) extending from the flap section (150) the expanding/contracting elastic member for the waist (520) and an attachment area (900) that receives the attachment section (300).
