The relation between radius-to-thickness ratios and non-axisymmetric plastic buckling patterns for axially compressed circular cylindrical shells was investigated from both analytical and experimental viewpoints. The obtained results are summarized as follows : (1) The lower bound value ( R / t ) _el (eq. (6)) of the radius-to-thickness ratios which produce the non-axisymmetric buckling pattern with n circumferential waves was determined by applying the elastic buckling theory, and its validity was confirmed through comparison with the experimental data given by Horton et al. (2) Numerical calculations of non-axisymmetric buckling stresses were carried out by using the simulator with 9 degrees of freedom which was composed of 6 rigid elements idealizing the periodic unit area of Yoshimura buckle pattern, and the value of ( R / t ) _pl (Table 1 and Table 2) was obtained corresponding to the circumferential wave number n. (3) It was certified that the value of ( R / t ) _pl can be almost considered as the lower bound to each circumferential wave number by conducting the compression tests for mild steel circular cylinders (Fig.10), however, more experimental data will be needed in order to establish the above conclusion.