Abstract: The effects of Ag on the wettability of Sn-9Zn lead-free solder and the mechanical properties of soldered joints are investigated respectively.The results indicate that when the content of Ag is 0.3 wt.%,the solder gets the best wettability;when the content of Ag is from 0.5 wt.% to 1 wt.%,the wettability decreases.The best mechanical property of soldered joint is obtained when the content of Ag is 0.3 wt.%.Moreover,the fracture micrographs show that plenty of dimples are found on the Sn-9Zn-0.3Ag soldered joints fractures.When the content of Ag is 1 wt.%,some Cu-Zn and Ag-Zn intermetallic compounds appear on the bottom of dimples,and the mechanical property of the soldered joint decreases.In general,the optimum additive amount of Ag in Sn-9Zn solder is about 0.3 wt.%.