Abstract: A variable structure control scheme which only uses the input-output measurements is presented in this paper. A strictly positive real comparison model and the state variable filters with logic switchings are introduced. Two cases where the relative degree of the modeled part of the plant is equal to one and greater than one are studied respectively. When the relative degree equals one, it is proved that the designed control system can implement the sliding mode control. A sign following system is used for the case when the relative degree is greater than one. It is proved that the designed control system guarantees the global stability. It is show that the proposed scheme is robust for systems with parametric uncertainties and unstructured uncertainties.