In the tests on brittle fracture of longitudinally welded wide plate specimens or welded spherical containers it was frequently observed that the propagating brittle crack in the direction oblique to the weld line changed its direction when the brittle crack approached to the welded joint, or the brittle crack initiated from the weld flaw was branched off and arrested by the base metal. The similar phenomenon was also observed in the brittle fracture of welded structures in a service condition. Consequently it may be considered that the residual stresses due to welding affect considerably the propagation of brittle fracture as in the case of initiation of brittle fracture. In order to study these effects of residual stresses on brittle fracture propagation, especially on the direction of propagation, the tests were conducted by using several types of welded plate specimens having an unsymmetrically placed longitudinal joint, adjacent two joints parallel to each other, or a diagonally placed oblique joint. The test specimen with a trapezoidally impressed artificial notch was fractured by applying impact under the temperature lower than the arresting temperature. The principal stresses in the welded specimens were measured in order to analyse the direction of brittle fracture. It may be concluded from the test results that the brittle crack propagates in the direction perpendicular to that of the maximum tensile stress resulting from the residual stresses due to welding and the applied stress, and the direction of brittle crack becomes unstable in the compression region of the resultant stress field.