As the Sn-8Zn-3Bi solder is hard and difficult to deform, the stress concentration which occurs in solder joints is high. And it is thought that the stress concentration is the reason why the brittle fracture occurs in and along the intermetallic compound layer. However, failure mechanism and fatigue strength in solder joints where different two solder materials were used are not yet known. In this study, failure mechanism in the composite construction solder joints was examined using the two-layer structure solder joints of Sn-3Ag-0.5Cu and Sn-8Zn-3Bi.