Abstract: This paper is concerned with active vibration control of building structures under seismic excitation. The reaching law method in the variable structure system (VSS) and sliding mode control (SMC) system is employed in the present analysis. Two sliding mode controllers are developed based on the constant plus proportional rate reaching law and the power rate reaching law. The controllers are extended by introducing saturated control method to avoid the adverse effect when the actuators are saturated due to unexpected extreme earthquakes. The simulation results are obtained for a three-storey shear building equipped with active brace system (ABS) under seismic excitations. It is shown that the present control methods are effective and promising in engineering practice.