In the previous study, the authors have discussed the fatigue strength of load-carrying fillet welded cruciform joints with no-penetration having critical leg-length proposed by Gurney, and it was found that the mode of failure were classified into three types of failure : weld failure, mixed failure and plate failure. In this study, an improvement of the fatigue strength was examined by fatigue tests under pulsating tension using the fillet welded cruciform joints of which the penetration was 5 mm in depth and other configurations were same as the cruciform joints used in the previous study. As a result, the following conclusions were obtained. (1) Change of the mode of failure in fillet welded cruciform joints can be explained by the estimation of the crack initiation life at weld toe, N _c ^T , the fracture life of plate failure, N _f ^T , and the fracture life of weld failure, N_f^T . (2) In as-welded cruciform joints used in this study, the effect of retardation of crack propagation from the weld root can be expected due to the residual compression stress near the weld root.