The invention relates to an active roll stabilization system for ships, including at least one stabilization element extending below the water line, which is mounted on a rotary shaft that extends through the ship's hull, a sensor for sensing the ship's movements and delivering control signals on the basis thereof to rotation member for rotating the rotary shaft for the purpose of damping the ship's movements that are being sensed through the stabilization element.The object of the invention is to provide an active roll stabilization system for ships that can be used both with ships which are underway and with ships that are at anchor. According to the invention, the active roll stabilization system is to that end wherein the stabilization element is provided with a sub-element that is movable with respect to the stabilization element. This makes it possible to impart an additional lifting moment to the ship via the stabilization element, both while the ship is sailing and while the ship is at anchor, for the purpose of effectively damping or countering the ship's movements that are being sensed.