A disposable diaper for pets, having: a diaper longitudinal direction； a diaper longitude-intersecting direction； a rear-side flap section； a stomach-side flap section； and a tail insertion opening provided in a prescribed area in the diaper longitudinal direction. The disposable diaper for pets is formed such that the length in the diaper longitude-intersecting direction in the rear-side flap section is different from the length in the diaper longitude-intersecting direction in the stomach-side flap section.
