Abstract: The remarkable variation of seismic responses of structures under strong earthquakes limits the implementation of performance based seismic design. Response variation may be caused by characteristics of ground motions and the seismic behaviors of structures. Based on numerical simulations, the influence of structural post-yielding stiffness on the seismic responses of multi-degree of freedom (MDOF) structural systems is discussed. By preventing stiffness degradation beyond elastic range, damage concentration in structures may be avoided, which would also reduce the variation of inelastic seismic responses. Moreover, it is found that structures with higher post-yielding stiffness are more effective to control the seismic performance of structures.