In this study, it is intended to determine the effects of soil-structure interaction (SSI) and spatially varying ground motion on the dynamic characteristics of cable-stayed bridges. For this purpose, ground motion time histories are simulated for spatially varying ground motions, depending on its components of incoherence, wave-passage and site-response effects. The substructure method, which partitions the total soil-structure system into the structural system and the soil system, is used to treat the soil-structure interaction problem. To emphasize the relative importance of the spatial variability effects of earthquake ground motion, bridge responses are determined for the fixed base bridge model, which neglects the soil-structure interaction (no SSI) and for the bridge model including the soil-structure interaction (SSI). This parametric study concerning the relative importance of the soil-structure interaction and spatially varying ground motion shows that these effects should be considered in the dynamic analyses of cable-stayed bridges. © 2011 Elsevier Ltd.