Abstarct: This research presents the mechanical design of a novel variable impedance actuator (VIA) for the knee rehabilitation exoskeleton, baxsed on a lever mechanism with adjustable pivot. Mechanism consists of two centralized hollow disks that are connected to motors by gears. Two disks are connected to the pivot by lixnk and adjust the position of pivot and output lixnk. Four linear spring are assembled on the rectangular frxame and are connected to the one side of the lever. Another side of the lever is connected to output lixnk by the output arm. In the proposed mechanism, for improving of the energy efficiency, the actuation and stiffness transmission systems are completely symmetric, therefore the energy loss and internal friction are reduced. With regard to the parallel configuration of the motors by means of two four-bar mechanisms, the actuator load is evenly distributed to each motor, and pivot is moved along the radial direction on a straight line without any linear guide. Due to the spring frxame, the spring’s deflection and output arms are perpendicular to each other, therefore the stored energy conversion to the output torque improves. Actuation performance investigated with simulation. Results demonstrate that the actuator with a different controller exhibits a good response and high accuracy for position regulation, stiffness regulation and tracking tasks.