The purpose of this paper is to verify the seismic strengthening effect of R/C buildings strengthened with the Carbon Fiber Composite Cable (CFCC) In this study, a three-story R/C building that constructed in the 1980s was selected, and its seismic performance before and after strengthening was evaluated based on the nonlinear dynamic analyses of members levels. The result indicated that the seismic strengthening effect of the proposed CFCC method was verified in terms of both strength and ductility demands, compared to the building before strengthening.