The seismic performance evaluation and retrofit process are very important in existing bridges. If the result is not appropriate, then retrofit process are required. Among various retrofit methods, the seismic isolation is a very useful method, because it can be applied by replacing old bridge bearings. In this study, the effectiveness of seismic isolation is rationally verified. For this purpose, two seismic isolations Used widely are selected and non-linear static and non-linear dynamic analyses are performed. The responses of existing bridges are compared with those of retrofitted bridge by seismic isolation bridge for earthquake of target level, and seismic performances are evaluated.