The wettability of Sn-Zn, Sn-Ag-Cu, Sn-Bi-Cu solder alloys on copper substrate was measured by sessile drop method. Among these solder alloys studied, the wettability of Sn-Bi-Cu alloy was excellent, at 530 K the contact angle between Sn-30Bi-0.5Cu alloy and Cu substrate was 26°. There was almost no contact angle hysteresis of the molten ternary eutectic Sn-3Ag-0.5Cu alloy. Adding Bi to Sn-based alloys could improve the wettability of alloys, while adding Cu could prevent the occurrence of dissolution of Cu substrate effectively. These research results may provide some theoretical basis for the use of lead-free solder alloys.