In this study, the seismic performance of a curved highway bridge having rectangular concrete piers and composite deck is evaluated by nonlinear elasto-plastic analysis method. The time-acceleration records of the Izmit (1999), San Fernando (1971) and Loma Prieta (1989) earthquakes which are modified corresponding to a probability of exceedance of 2% in 50 years are used in the analysis. According to the analysis results, strengthening of the bridge is required. In the strengthening strategy, the viscous dampers are mounted on each bearing at the top of the piers in the transverse direction by preserving the existing architectural appearance of the bridge as much as possible. Thus the relative displacements between the composite superstructure and the piers are limited, and the internal forces which occur in the piers and foundations are reduced.