This paper deals with an experimental study on the interactive buckling behavior of steel compression members with thin-walled stiffened box cross section. In this study, attention is paid to the interactive behavior of local plate buckling and global column buckling, the ultimate strength, and the ductility of the steel compression members. The local plate buckling consists of the buckling of component stiffened plate panels, local plate panels between longitudinal stiffeners, and longitudinal stiffeners. Axial loading tests are carried out for the scaled down column specimens with variouswide-thickness ratio of the plate panels and the slenderness ratio as columns to investigate the interactive behavior. Indices for deciding the occurrence of the bucklings are proposed by using various strain data at the middle cross sections of the specimens and the buckling phenomena of the specimens are investigated regarding the global buckling, the local plate buckling and their interactive buckling by using the indices. Effectiveness of these indices is discussed here in.