Generally, the active structural control system belongs to the discrete time control system, and the sampling period is one of the most important factors that would directly affect the performance of tbe control system. In this paper, active control approaches by using the discrete-time variable structure control theory are studied for reducing the dynamic responses of seismically excited building structures. Based on the discrete reaching law method, a feedback controller which includes the sampling period is presented The controller is extended by introducing the 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 single-degree-of-freedom (SDOF) system and a MDOF shear building equipped with active brace system (ABS) under seismic excitations. It is found that the discrete variable structure control approach and its saturated control method presented in this paper arc qu0e effective.