This paper presents a comprehensive investigation on viscous wall dampers (VWD) used for seismic response mitigation of reinforced concrete (RC) frames. First, a shaking table test on a large-scaled three-story RC frame with VWD and another identical three-story RC frame without any dampers was carried out. A total of three types of earthquake excitations were inputted to the shaking table to evaluate the effects of VWD on seismic response mitigation. The influence of different earthquake input intensities on seismic performance of VWD were also examined. From the experiment, this paper further assessed the performance of VWD on seismic retrofitting of a partly damaged RC frame. The test results show that the main effect of installing VWD is to provide a large amount of supplemental damping to the RC frame, and at the same time the stiffness of the structure is also raised moderately as an accessorial effect. As a result, the displacement responses of the RC frame can always be reduced significantly, while the acceleration responses and the base shear of the RC frame were reduced in some test cases, but increased in other cases. The test results of seismic retrofit also show that seismic responses of the damaged RC frame can be alleviated evidently by the installation of VWD and, therefore, installing VWD is an effective retrofitting approach for RC frames. After test investigation, elastic and inelastic seismic responses of the RC frame were numerically simulated using finite element software Sap2000 and Canny99, respectively. A good agreement of experimental results and analysis results verified the analytical method and model used for RC structures with VWD.