In the previous report, it was revealed that the effects of high temperature prestraining on the retained ductility and notch toughness of various structural high tension steels were generally slighter than those for mild steels. In this paper, the characteristics of fracture stress curves were investigated on five high tension steels whose tensile strengths were ranging from about 50 to 80 kg/mm², and also on two special structural steels for low temperature use, and compared with the results of previous report2) 12) for mild steels. Concerning the natures of both fracture stress curves, cleavage and fibrous, important informations were clarified as follows : (1) The shapes of both fracture stress curves were practically similar in each steel. Also those shapes were approximately same for every steel tested. The height of fibrous fracture stress curve was nearly proportional to the nominal tensile strength. (2) A good relationship was found as shown in Fig. 22 between the height of both fracture stress curves and transition temperature in V-Charpy test, using a reasonable parameter in Eq. (7). (3) An excellent notch toughness of quenched and tempered steel was chiefly attributable to the rise in fracture stress curve by this heat treatment observed remarkably for cleavage type one. Such behavior in stress curves should be favorable to the notch toughness judging from the above relationship.