For three large cable-supported bridges, namely the Yokohama Bay Bridge, Rainbow Bridge and Tsurumi Tsubasa Bridge, a study on seismic retrofit to resist level-2 ground motions was made. For the bridge components that were expected to be damaged in view of the response values obtained by nonlinear dynamic analyses, the ultimate strength and maximum deformation capacity were further calculated by inelastic analyses using a three-dimensional finite element method. Based on these analyes, a damage tree in the bridge system was prepared. Then, retrofit designs were considered to limits the damage to be an allowable.