This paper is concerned to constitute a semi-active realtime feedback vibration control system and evaluate it through experiments in order to control in realtime the vibration externally generated, specially on the bridges which is structurally flexible. For the experiment of vibration control, we built a model bridge structure of Seohae Grand Bridge in a 1/200 reduced form and inflicted El-centro wave on the model structure also in a reduced force considering the lab condition. The externally excited vibration was to be controled by placing a shear type MR damper vertically on the center of bridge span, and the response (displacement and acceleration) of structure was to be acquired by placing LVDT and Accelerometer at the same time. As for the experiment concerning controlling vibration, a realtime feedback vibration control experiments were performed under each different condition largely such as un-control, passive on/off control, Lyapunov stability theory control, and Clipped-optimal control. Its control performance under different condition was quantitatively evaluated in terms of the peak absolute displacements, the peak absolute accelerations and the power required for control on the center of span. The results of experiments proved that the Lyapunov control and clipped-iptimal control were effective to decrease the displacement and acceleration of the structure, and also to decrease the power consumption to a great extent. Finally, the semi-active realtime feedback vibration control system constituted in this research was proven to be an effective way to control and manage the vibration generated on bridge structure.