To isolate the mounted object from the vibration sources, it is required that the qualities of the actuators in an active vibration isolation system are highly promising. Therefore, it is unreasonable to ignore actuator nonlinearity to realize the excellent performances of the vibration isolation. In this paper, the problem of unknown actuator backlash in the vibration isolation system is investigated. To handle the lines-segments backlash nonlinearity, an adaptive smooth backlash inverse is employed to compensate the deleterious effect. Moreover, a promising controller is proposed to ensure that the motion of the moving platform converges to desired values. Based on Lyapunov's second method, all of the involved signals in the closed-loop system are proved to be stable. Finally, comparative studies involving active vibration isolation with actuator backlash are constructed and carried out to validate the effectiveness of the proposed control scheme.