An animal litter box having a fall length of animal liquid excrement shortened as much as possible. The animal litter box (1) has a transverse direction (X), a longitudinal direction (Y) and a vertical direction (Z) and includes a lower container (30) having an opening (31) at an upper end thereof and allocated on the lower side, an upper side cover (10) allocated above the lower container (30) and a liquid passable litter tray (20) interposed between the upper side cover (10) and the lower container (30) and cooperating with the lower container (30) to close the opening (31), thereby defining a receiving space (2) in such a manner that the liquid passing from the upper space is assured. The lower container (30) has an excrement tray (40) provided so as to be manuallymovable in the longitudinal direction Y between a put-in position at which the excrement tray (40) is set within the receiving space (2) below the liquid passable litter tray (20) and a drawn out position outside the receiving space (2) and an end opening (33) through which the excrement tray (40) is put into or drawn out from the receiving space (2). The excrement tray (40) hasabottomwall (41) shaped in a rectangle as seen in its planar view and side walls formed along a peripheral edge composed of four sides of the bottom walls (42a, 42b) and adapted to be put in contact with flaps (54a - 54d) extending along a peripheral edge of the absorbent structure (50). A pair of the side walls (42a, 42b) is formed in a tilted manner so as to be gradually distanced from each other as the side walls extend upward.
