Abstract: A cat litter box has a housing and a tray. The housing has a bottom segment and a top segment. The bottom segment has a lower chamber, a front open end and a slope. The slope is formed in the lower chamber. The top segment is formed on the bottom segment and has an upright passage and a front entrance. The upright passage is above the slope. The tray is mounted in the lower chamber through the front open end. The cat litter box is configured to provide litter-cleaning procedures to cats so that a cat may drain in the cat litter box without bring inadvertently out litter particles to pollute everywhere to result in frequently cleaning of the indoor environment.