A pet litter box (1) comprises a base element (10) having a support surface (11) for a pet, an absorbent mat (20) laid on the base element (10), and an open-top frame (30) removably mounted to the base element (10). The frame (30) has a bottom wall (31) associated with the base element (10) with the absorbent mat (20) thereon. The bottom wall (31) has an opening (32) in such position as to entirely overlap at least one portion (21) of the absorbent mat (20), and at least one side wall (35) that extends vertically from the bottom wall (31) to define an entrance (33) for a pet into such portion (21) of the absorbent mat (20).
