A cat litter box assembly having a base tray and an insert. The base tray has opposing side walls and a front wall. The front wall has a height less than the opposing side walls to define a partially open end of the base tray. The insert has a bottom wall and opposing side walls. The bottom wall has a plurality of openings formed in a portion thereof and a leading edge that extends between ends of the opposing side walls. The leading edge of the bottom wall and ends of the opposing side walls define an open end of the insert. The insert is insertable into the base tray through the partially open end of the base tray such that the leading edge of the insert engages and slides along the bottom wall of the base tray as the insert is inserted into the base tray.