The authors previously presented a paper on the influence of the residual stresses on the buckling loads of the compressed mild steel plates in the elastic, elastic-plastic and plastic ranges. In these days, there is a tendency to use widely the high tensile steels to the ship structures, and it becomes important to clarify the effective method to use them. In this paper, it is treated the buckling strength of hibrid plates which are constituted by mild steel and high tensile steel, and the influence of residual stresses on it. The foundamental assumptions of theoretical analysis in this paper are identical with those in the previous paper. Experiments were carried out in the following for main series of specimens (supported along all edges and the dimenssons of 1200 × 580 ×814 mm), i. e. C-series (the center plate of three equi-width plate-elements is high tensile steel and the end plates are mild steel), CA-seriei (the residual stresses are excluded by annealing C-series), E-series (the center plate is mild steel and the end plates is high tensile steel), and EA-series (the residual stresses are annealed). In addition the effectiveness of the high tensile steel plates when used as compression member was studied. Conclusively it may, theoretically and experimentally, be said that the residual stress pattern in tsis paper makes the buckling loads increase slightly in the elastic range and E-series, add has small influence on C-series, generally the influence is smaller than in previous paper, and that εδ² method is effective, and that as for the effectiveness of high tensile steel, it is economical to use the mild steel, H. T. 50 and H. T. 60 according to the given external load and the width of plate.