In this paper, a dynamic stress analysis of seismic vibration isolator was carried out by using ANSYS. The vibration isolator consisted of Si-Cr springs and magnetorheological dampers. The stress and deformation of the springs were calculated when an impact load was applied to the isolator. From the simulation for six different springs, in terms of their wire dimeter and coil diameter, an optimum shape of the springs to minimize the stress and deformation was determined.