Passivity has been the most often used constraint for the controller design of bilateral teleoperation systems. However passivity has been suffering from its own design conservatism since this is a sufficient condition for stability and representing only a small set of overall stability region. In our previous works , , a less conservatism control approach, we named it Input-to-Sate Stable (ISS) approach, has been introduced for reducing the intrinsic design conservatism of the passivity-based controllers by allowing bigger output energy compared with the passivity-based controller while guaranteeing the stability. However the previous works were limited to haptic interfaces, which is interacting with computer generated virtual environments. In this paper, we extended the ISS approach for bilateral teleoperation systems. For this extension, the previous one-port ISS approach was generalized to two-port ISS approach. The main difficulty of this extension was identifying the signal pair to show hysteresis nonlinear behavior. By introducing a linear function assumption for two-port bilateral controller, which is generally acceptable, we could formulate two-port ISS approach. The extended two-port approach was implemented to a position-force bilateral teleoperation system, and the performance was experimentally verified with a dual Phantom teleoperation system.