Abstract: A hydraulic jack for providing safety security is disclosed. The hydraulic jack comprises a hydraulic cylinder storing hydraulic fluid inside, and a piston installed in the hydraulic cylinder that is raised up from the hydraulic cylinder by a pressure of the hydraulic fluid stored in the hydraulic cylinder, thereby a heavyweight can be lifted by the piston. The piston has a drill hole on a body thereof that has a determined diameter and is perpendicular to the piston. When the piston is raised up, a safety pin is penetrable through the drill hole to secure the piston in place.