Dynamic analysis of guyed tower is presented in this study. The scope of the study is twofold. The one is to determine an efficient method to include the nonlinearity of the mooring system and the nonlinear hydrodynamic wave forces. The other is to investigate the sensitivity of two major design parameters, that is the stiffness of mooring system and the fixity condition of the tower at mud line. Analyses are carried out using the Lena Guyed Tower, which is the first structure of this kind, as a standard model.