Abstract: In this paper, the efficacy of semi-active hybrid control system for seismic protection of cable-stayed bridge is examined. The investigation is carried out on a simplified lumped mass finite element model of the Quincy Bay-view Bridge at Illinois. The bridge is isolated using a high damping rubber bearing (HDRB) along with the semi-active magnetorheological (MR) damper to form semi-active hybrid control system. For the MR dampers, a control algorithm based on the Lyapunov stability theory is employed. The HDRB is modeled with linear spring and dashpot; and various dynamic models, such as a Bingham model, a Bouc-Wen model, and a modified Bouc-Wen model are used for the MR damper. The bridge is also analysed under the variation of command voltage input to MR Damper. The results of semi-active hybrid system are compared with those obtained with passive hybrid systems composed of isolation with passive viscous damper. The simulation results indicate that the performance of the semi-active hybrid control system is better than that of the system with passive hybrid systems. Further, it is also observed that the variation in command voltage to MR damper has significant effects on the response of the bridge.