Abstract: The low cycle fatigue properties of 63Sn-37Pb and Sn-3Ag-0.5Cu alloy solders at torsional load were studied by torsional fatigue tester. The results show that the two solders are cyclic softening materials and their deformation is dominated by plastic deformation. The fatigue life of the alloy solders all increased with decreasing the shear strain amplitude. Moreover, the fatigue life of Sn-3Ag-0.5Cu solder was longer than that of 63Sn-37Pb solder at the same shear strain amplitude, indicating that the former had higher resistance to shear fatigue failure.