The brittle fracture initiation in butt welded joints of two kinds of 80 kg/mm² class high strength steels has been studied using wide plate specimens each of which had a surface notch along the weld bond and was given the weld angular distortion. Effects of the residual stress adding, the offset and the ACI (Anti-Crack-Intiating) beads on the brittle fracture initiation characteristics in such a specimen has also been studied. It has been found that the residual stress adding made it easy at higher temperature for the specimen to failure under low applied stress and that the ACI beads shifted the fracture stress transition temperature to extremely lower temperature. The effect of a offset on the fracture stress transition temperature was extraordinary remarkable, and has been clalified quantitatively by means of a newly developed K_I equation. This equation makes also it possible to express the effects of surface notch size, amount of angular distortion and another various kinds of conditions on the brittle fracture initiation characteristics of the welded joint. Furthermore the effects of weld heat input and chemical composition of steel on the fracture initiation characteristics of the weld has been cleared through experiments and the K_I equation.