Abstract: To improve seismic properties, some existed concrete frames are retrofitted with Buckling-Restrained Brace (BRB). Considering the insufficient seismic-bearing capacity of the original structures, in-filled steel frames and connected BRBs are used to retrofit. Three concrete frames are designed, built and tested. Two of them are retrofitted with in-filled steel frames and BRB (BRBCF), and the other one is an ordinary frame, which is designed for a comparison. Seismic performance of the frames, including the shear force-lateral displacement hysteretic curves, the skeleton curves, the axial deformation loops, the statistics on equivalent stiffness and the damping ratios, are tested and studied. The results of the tests show that the force-displacement hysteretic curves of the retrofitted frames are stable in shape; the BRB#x02019;s energy-dissipation ability is stable. It is proved that the load-bearing capacity and structural damping can be both increased in this way. Consequently, the in-filled steel frames can balance the load-bearing capacity of BRBs, which protect the original frames from suffering more severe shear force, excavate the potential ductility of the reinforced concrete floor and beams, and improve the working mechanics. The seismic performance is improved obviously