Abstract: Based on Sn-3.8Ag-0.7Cu lead free solder,the effect of cerium on the wettability and mechanical properties of soldered joints were investigated by means of Solder Checker STA-5100 and STR Joint Strength Tester.The results showed that the wettability of solder can be improved by adding small amount of Cerium and the optimum was in the range of 0.03wt.% to 0.05% wt.With the rising of testing temperature,the wettability is greatly improved gas well as by adding nitrogen.Adding small amount of Cerium to Sn-3.8Ag-0.7Cu lead free solder,the mechanical properties of soldered joints is enhenced and the optimum is about 0.03% wt.