Abstract: An improved animal sanitary litter box comprising a pair of identical matingly interfitting stackable trays, each of the trays including a slidably movable bottom panel which is movable between a first, closed position for retaining a quantity of litter, and a second, open position. Litter is sifted downwardly from an upper tray to a lower tray, while solid animal excrement is retained on the bottom floor of the upper tray. The excrement can be discarded, the tray cleaned, and then returned to the lower position of the pair of trays. The tray into which the litter was sifted can then be placed atop the now-clean first tray and the litter reused. The size of the openings defined by the movable bottom panel and the floor of the tray is selectively variable for better sifting.