A method of analysis is developed for coupled free oscillations of suspension bridges in three dimensions. The method, which is based on a finite-element approach, takes into account the nonlinear coupling effects by means of considering the finite displacements of the main cables and the hangers. The accuracy and efficiency of the proposed method are demonstrated by comparing the computed results with the experimental values and the previously computed values reported in Refs. 18, 19. The nonlinear-coupled characteristics in the torsion-dominant first mode are also investigated for a suspension bridge under construction and a suspension bridge deformed by wind forces.