Abstract: Effects of rear-earth element Ce on physical properties,wetting properties,tensile strengths and microstructures of Sn-3.5Ag-(0.5Cu) lead-free solder were studied.Results indicate that its conductibility will be improved and its density will decrease if Ce is added into the leadfree solder.In the range of 0.03%wt. to 0.05%wt. of Ce,the wettability of the solder is improved,especially when the content of Ce is about 0.03%wt.,the grains of the micro structure in lead-free solder are smaller and more homogeneous and the tensile strength of the soldered joints is higher than that of the solder containining other contents of Ce.When the content of Ce is more than 0.1%wt.,it is harmful to the properties of the Sn-3.5Ag-0.5Cu solder,the wetting time becomes longer,the values of the tensile strengths of the soldered joints become much lower.All of the results show that the optimal content of Ce in Sn3.5Ag-(0.5Cu) solder is about 0.03%wt.