This paper presents hybrid control systems for seismic protection of a phase II benchmark cable-stayed bridge. Because multiple control devices are operating, a hybrid control system could alleviate some of the restrictions and limitations that exist when each system is acting alone. In this study, two types of hybrid control system are considered to protect the cable-stayed bridge under seismic events. Lead-rubber bearings are used as passive control devices to reduce the earthquake-induced forces in the bridge and hydraulic actuators or magnetorheological fluid dampers are used as additional control devices to further reduce the bridge responses, especially deck displacements. Numerical simulation results show that the performances of the proposed hybrid control systems are superior to those of the passive control system, and slightly better than those of the active or semi-active control system alone. Furthermore, it is verified that the hybrid control systems are robust to mass or stiffness parameter perturbation, and there is no sign of instability in the overall system due to the passive control part. Therefore, the proposed hybrid control systems could effectively be applied to seismically excited cable-stayed bridges. Copyright ？2003 John Wiley & Sons, Ltd.