The purpose of this study is to investigate the effect of ice on the seismic response and dynamic stability against sliding of a large-scale off-shore structure that is surrounded by thick ice. The nonlinear soil-structure-ice interaction system was analyzed by the two-dimensional finite element method. In modeling the system, a modified joint element was employed to simulate sliding phenomena at the interface between the soil and the structural base. Three accelerograms having different predominant frequencies were used as input motions to examine the effect of frequency on the structural response and stability. Three different values of Young's modulus were used for the ice. It was found from the analyses that the ice decreased the seismic response of the structure and increased the stability against sliding.