Abstract: A simplified yet effective design procedure for viscous dampers was presented based on improved capacity spectrum method using the concept of performance based seismic design. The amount of added viscous damping ratio required to meet a given performance objective was evaluated from the difference between the total demand for effective damping ratio and the inherent damping ratio plus equivalent damping ratio resulting from hysteretic system deformation. Application of the method is illustrated with two examples, using Chinese design response spectrum and mean response spectrum. Nonlinear dynamic analysis results indicate that the maximum displacements of structures installed with supplemental dampers designed in accordance with the proposed method agree well with the given target displacements. The advantage of the presented procedure over the conventional iterative design method is also highlighted.