A foldable litter box and a litter box with a variable volume are provided. The foldable litter box includes a bottom plate and a several side plates integrally formed with the bottom plate, the side plates can be bended relative to the bottom plate to enclose a housing cavity. The side plates includes a front baffle and a rear baffle, as well as a left baffle and right baffle. The foldable litter box also includes connection plates integrally formed with the front baffle and the rear baffle, and the connection plates can be bent and connected to the left baffle and the right baffle respectively. The litter box can be quickly transformed into a pet litterbox with different volume from a flat state to different folded states, and the litter box can be quickly returned to the flat state when not in use, thus reducing space occupation.