Abstract: Magneto-rheological (MR) dampers are applied in this study to restrain structural vibration. A time delay dynamic model of the MR damper-stay cable system is derived using the Galerkin method. Stability conditions of the system are investigated via modal and linear stability analyses. Numerical results show that the time delay can diminish the performance and stability of the vibration control system. For a certain gain, the performance of the system can be weakened as the value of time delay increases.