An animal litter box includes: an upper container, which having an upper opening for animals to come in and out, and a bottom portion, which allows fluid to pass through and over which particulate matter is spread； and a lower container having a lower opening provided below the bottom portion, and a holding portion for disposing a fluid absorbing sheet container in which the fluid absorbing sheet which absorbs fluid passing through the bottom portion is laid, wherein a fitting portion for fitting to an edge of a lower opening of the lower container is provided at a side or bottom of the upper container. The fitting portion is preferably a stepped portion or a concave portion.
