This study presents the response mitigation effect of piping systems by inelastic seismic design based on elastic-plastic property of steel pipe supports. The inelastic seismic design to control vibration by absorbing energy using elastic-plastic properties of materials can be one of useful ideas. The design idea to use the elastic-plastic behavior of pipe supports is addressed in Technical Code for Seismic Design of Nuclear Power Plants (JEAC4601) published by the Japan Electric Association in Japan. Here, the component named an elastic-plastic pipe support is proposed as an energy-absorbing element. However, in order to put the inelastic seismic design using the elastic-plastic pipe supports into practical use, it is necessary to accumulate more findings related to the seismic response and the application range. This study aims to investigate the applicability of the inelastic seismic design taking the elastic-plastic pipe supports in the piping systems and to increase the basic findings. In this study, the seismic response analysis using three-dimensional piping system with an elastic-plastic pipe support was conducted. As a result, it was found that the elastic-plastic pipe support affected the seismic response largely. Additionally, the vibration characteristics, the response acceleration, and the load generated in the piping system were discussed relating to the plastic deformation and the plasticity rate of the elastic-plastic pipe support.