The influence of the feed concentration on the progressive changes in concentration profiles along the simulated moving bed (SMB) columns and in the concentration histories at the SMB outlets during the transition of the SMB operation toward steady state is Studied. This investigation is concerned with what happens when tile isotherms of the two components of the feed in the phase system have competitive Langmuir behavior and the feed concentration is raised froth the linear to the nonlinear range. In order to achieve a clear comparison between the SMB behaviors in the nonlinear and the linear case, the flow rates in all the sections of the SMB are kept constant, at the same value of these operation parameters as selected in the linear case. Transition concentration profiles to the steady state were examined as functions of the degree of nonlinear behavior, i.e. for different values of the reduced concentrations of the feed components, b(i)' = b(i)C(i). The profiles obtained in the linear and nonlinear case are compared to illustrate the nonlinear effects. Square-wave oscillations of the plateau concentrations of the extract in column II and the raffinate in column IV, due to the cyclical nature of the SMB operation, have been reported previously in the linear case. This phenomenon is discussed in the nonlinear case and the influence of the switching time is illustrated.