Owing to the toxicity of lead, the majority of packaging of electronic products is now fabricated using lead-free solders. Impact resistance of lead-free solder joint has attracted significant interest in recent years due to the widespread use of mobile electronic products. Ball impact test has been widely adopted in measuring the impact resistance of the solder joint. It is reported that the growth of the IMC layer degrades the impact resistance of the solder joint. However, evaluation of impact resistance is not conducted in terms of morphology of fracture surface. This study aimed to clarify the effect of IMC layer thickness on impact resistance of the solder joint in terms of morphology of fracture surface. For this purpose, Sn-3.0Ag-0.5Cu and Sn-1.0Ag-0.5Cu were soldered on electroless Ni-P plating (Ni-P). And then, some of the specimens were subjected to the isothermal aging at 423 K for 168-504 h. After aging, the IMC layer thickness was measured using an optical microscope (OM). The miniature ball impact test was then carried out to evaluate impact resistance of solder joint. After the impact test, fracture surface on pad side was observed by the OM. The results showed that the IMC layer thickness increased with increasing aging time. The both Sn-Ag-Cu solders formed Cu6Sn5 type IMC including Ni. The fracture occurred at the interface between solder and Ni-P at the impact side, regardless of the aging conditions. Some residual solder remained at the opposite side of the impact. The area fraction of the interfacial fracture increased with increasing aging time, and the fracture energy of the solder joint decreased with increasing aging time. This study found that the interfacial fracture is easily achieved by the growth of the IMC layer, and the growth of the IMC layer degrades the impact resistance of the solder joint.