The influence of column stiffness on the modal contribution in the transverse direction of singe-column bent viaducts in the nonlinear range is investigated in this paper. The modal contribution ratio is introduced as a measure of the importance of a mode after a bridge yields. Three typical mathematical models of irregular singe-column bent viaducts are selected for analytical seismic response. The comparative evaluation of modal contribution ratios are carried out when columns with different stiffness yielded individually. Results show that yielding of a stiffer column affects the contribution of the fundamental mode as well as that of the higher modes significantly while the yielding of a more flexible column affects the modal contribution of the fundamental mode only.