In this study, the relationship between microstructural change and fracture in the process of low-cycle fatigue of Sn- Ag-Cu solder joint was investigated using the solder ball of 630 μm and 100 μm in diameter by analysis of crystallographic orientation by means of EBSD. The 630 μm specimen has subgrain boundaries formed by dynamic recovery in the stress concentration region, and the subgrain boundaries become highangle random grain boundaries by additional cycles. The fatigue crack stably propagates along the random grain boundary in the stress concentration region. In contrast, the 100 μm specimen has subgrain boundaries and high-angle random grain boundaries formed across the entire joint area. Since the occurrence of grain boundary fracture across the entire joint area by the connection of high energy grain boundaries, the crack propagation life of the 100 μm specimen shortens without the stable crack growth compared to the 630 m specimen.