The fourth series of test was performed to investigate the effect of residual welding stress on onttle fracture fracture of steel, especially on the propagating direction of brittle crack. Oblique welded specimens were prepared and half of them were stress relieved by annealing. Fracture test procedure was same as slow notch bend test. In as-welded specimens, propagating directions of britte crack were deviated at welded joint, but in annealed specimens, there was little deviation. To show the change of principal stress direction, photoelastic experiment was also performed. Our former conclusion that residual welding stress effects on brittle fracture, was recognized in such a problem-propagating direction of brittle crack.