Abstract: The difference of dynamic characteristics and seismic responses between cable-stayed bridges with steel and carbon fiber composite (CFRP) cables was studied and the essential reason was investigated, taking the northern channel bridge of Hangzhou bay as an object. The steel cables were replaced with CFRP cables using strength equivalent principle and the program for seismic response calculation considering cable lateral vibrations was employed. The results show that coupling vibration between bridge and cables is the essential reason inducing the difference of dynamic characteristics and seismic responses between the bridges with two kinds of cables. The frequencies for free vibration of CFRP cables are higher, so the possibility of cable-bridge coupling vibration is smaller than that of steel cables. The seismic responses of cable-stayed bridges with CFRP cables are lower than that of steel cables under the same seismic loadings.