In the previous reports, the effect of the design factor such as arrangement of spot welds on the strength of joints has been clarified. The presentstudy deals with the effect of the defective spot welds of as one of the factors affecting the strength of joints which is as effective as design fsctor. In this report, in order to obtain basic data for the purpose, the relationships between the internal defects such as crack, porosity, or expulsion on Radiography testing, and the strength or distortion-coefficient of spot weld, was investigted for Al alloy spot welds under static or repeated shear load. As the result of this study, these relations have been clarified, that is, the average strength of spot weld was not so markedly influenced by the internal defects within the region of d/D≤0.3 nearly (d: dia. of the region, D: nugget dia. of spot weld), but only when the spot weld was a stiffener joint, the fatigue strength greatly decreased; moreover, the effect of internal defects on distortion-coefficient is noticed more or less.