Abstract: A fire hydrant automatic shut-off valve including a cylindrical sleeve having an open lower end and an open upper end. The open lower end receives a water supply stand pipe therein. The open upper end receives an open lower end of the fire hydrant thereon whereby the open lower end of the fire hydrant is in communication with the water supply stand pipe. A pair of flaps is hingedly coupled with the open upper end of the cylindrical sleeve. The pair of flaps close to a corresponding horizontal position to effectively seal the cylindrical sleeve to prevent water from flowing from the water supply stand pipe to the fire hydrant. A trigger sleeve is slidably disposed within the open upper end of the cylindrical sleeve. The trigger sleeve extends downwardly to push the pair of flaps outwardly to allow water to flow freely from the water supply stand pipe to the fire hydrant.