Recently the fracture mechanics analysis is often used as a means to verify the structural safety and soundness. In making the fracture mechanics analyses, the existance of crack should be firstly assumed and then the growing behavior of the crack is calculated and predicted. Most of the characteristics of the crack behavior are theoretically analysed and experimentally confirmed, however, some of the else are expediently assumed by the lack of the informations. One of these uncertainities, for example, is the fatigue crack path which have propagated toward the fillet weld line on the plates intersections. In these circumstances, the authors investigated fatigue crack propagation behaviors at fillet weld on plates intersections, by conducting I-shaped section beam bending tests and stiffened plate tensile tests. And they tried to characterize the fatigue crack path in relation to the crack attack angle to weld line, the weld leg length, the flange stiffness and so on. Resulting from the experiments, it has been verified that cracks propagate almost exactly to the normal direction to the maximum principal stresses before the crack tip reaches to the weld reinforcement. And when the crack tip comes to the weld line, it can be roughly classified by several parameters whether the crack goes across the flange plate or turns its direction and goes along the weld line. Namely, the experimental chart to estimate fatigue crack path was obtained using the maximum principal stress at crack arrival point on weld line and the shearing stress along the fillet weld throat section.