Abstract: An automatic lavatory seat comprises a mounting seat secured to the lavatory pan, a lavatory seat connected with said mounting seat by means of a pivot pin, a coil spring around said pivot pin for raising said lavatory seat, a plunger secured at one of two opposite sides constituted by said lavatory seat and said mounting seat while a flexible hose is secured at the other, and a pneumetic valve at one end of said flexible hose, being characterized in that on removal of the load upon said lavatory seat, said flexible hose with said plunger fitted therein will resist the force exerted by said coil spring, thus producing a time lag in the return movement of said lavatory seat.