Series of elastic eigenvalue analyses and elastoplastic large deflection analyses were performed to investigate into the influence of perforation on the buckling/ultimate strength of rectangular plate subjected to uni-axial and bi-axial thrust. It has been found that : (1) Beyond the ultimate strength, plastic deformation is concentrated around the opening, and elastic unloading takes place in the remaining part in case of long plate subjected to longitudinal thrust. (2) Beyond the ultimate strength, plastic mechanism of a roof mode developes in case of long plate subjected to transverse thrust. (3) Ultimate strength interaction relationship is derived for bi-axial compression, and it was found that general yielding at the perforated cross-section affects the shape of the interaction curve. Simple formulas are proposed to evaluate the elastic buckling strength of a perforated plate under uni-axial thrust. These formulas are used to evaluate the ultimate strength, which showed good correlations with the FEM results.