In order to investigate the effect of notch radius on the brittle fracture of steel, slow notch tensile tests were performed. Rimmed, semi-killed and HT 52 high tensile steels were tested. Test specimen used is shown in Fig. 1, and notch radii were varied in six stage, 0, 0. 05, J. 1, 0.25, 0.5 and 1.0 mm. Transition phenomena of shear fracture percentage, stress, elongation, energy absorption and reduction in thickness are shown in Figs. 2-9. Effect of notch radius on various transition temperatures can be seen in Table 3 and Figs. 10-12. In notch tensile test, smaller notch radius might be more preferable to know both of fracture and ductility transition properties of steel.