Abstract: 7 groups of asynchronous ground acceleration time histories of Chichi earthquake,Taiwan,Sept.21,1999,recorded by a dense closely spaced array SMART-II with GPS international standard time calibration,and 2 groups of synthetic asynchronous acceleration time histories generated by using a hybrid method of mode superposition and finite difference are used as earthquake ground motion inputs,to analyze earthquake responses of Sutong cable-stayed bridge with the longest span in the world.Different angles between the longitudinaldirection of the bridge and wave traveling direction or direction of Chelonpu fault,and cases of fault-crossing or fault-no-crossing of the bridge are considered.The responses are compared with those to related synchronous seismic ground motions consisting of those with the largest peak ground acceleration in each group of inputs.The results show that responses of such a long-span bridge to asynchronous seismic ground motions are very likely to be larger and sometime much larger than those to related synchronous seismic ground motions.Therefore,seismic design of such long-span bridges should consider effects of asynchronous seismic ground motions.The paper also evaluates quality of synthetic ground motion time histories given by a concerned institute with respect to response spectra and cross-correlation coefficients between synthetic time histories.The results show that bridge designers must check quality of the synthetic time histories.