Under severe earthquakes, plastic deformation of members should be controlled from the viewpoint of safety and repairability, though yielding of structures need not be avoided. In seismic designs, deformation of structures and members is estimated by nonlinear analysis. Therefore, the accuracy of a hysteresis model employed in the analysis influences the reliability of design. In this paper, we propose a tetra-linear hysteresis model of reinforced concrete members. This model has three turning points and a descent slope in the postpeak region. Seismic response of structures can be estimated by using this hysteresis model even after some members have reached the postpeak region.