In recent years, from the viewpoint of the improvement of environmental performance and collision safety, it is demanded for vehicle structure to be light-weight and to have high rigidity. Then, thin walled structure is used for vehicle structure as a main frame to satisfy these requirements at the same time. The purpose of this study is to investigate the elastic-plastic buckling phenomenon of thin walled rectangular tubes by pure bending. Thin walled rectangular tubes have various configurations of cross section to change the stiffness of side wall. Hence, the influence on deformation property by the difference of the configuration of cross section is discussed experimentally. And the critical buckling stress and the behavior after pre-buckling are cleared by numerical analysis.