Effects of micro-amount of rare earth Ce on microstructures of Sn-3.0Ag-0.5Cu solder alloy were studied. The results indicate that microstructures of Sn-Ag-Cu-Ce solder alloy are composed of Sn-rich phase and eutectic structures, including two binary eutectic structures (granular Cu6Sn5+β-Sn and needle-like/flake Ag3Sn+β-Sn) and one ternary eutectic structure Cu6Sn5+Ag3Sn+β-Sn emerged among β-Sn dendrites, some intermetallic compounds (IMC) and Ce compounds also exist. Microstructure of solder alloy becomes finer with the increase of the content of Ce, and the optimum content of Ce is about 0.03%, the binary eutectic of needle-like/flake Ag3Sn+β-Sn becomes fine equiaxed crystal; coarse compound phases exist when the content of Ce is up to 0.1%, which is harmful to microstructures of solder alloy and soldering seam. With regard to soldered joints, microstructures formation of the interface between Sn-Ag-Cu-Ce solder and Cu substrate (soldering seam) is different from that of Sn-Ag-Cu-Ce alloy itself, as a result of different cooling speed and dissolution of Cu into solder alloy. Effects of micro-amount of rare earth Ce on microstructures of Sn-3.0Ag-0.5Cu solder alloys were studied. The results indicate that microstructures of Sn-Ag-Cu-Ce solder alloys are composed of Sn-rich phase and eutectic structures, including two binary eutectic structures (granular Cu6Sn5 + β-Sn and needle-like / flake Ag3Sn + β-Sn) and one ternary eutectic structure Cu6Sn5 + Ag3Sn + β- Ce compounds also exist. Microstructure of solder alloys becomes finer with the increase of content of Ce, and the optimum content of Ce is about 0.03%, the binary eutectic of needle-like / flake Ag3Sn + β-Sn becomes fine equiaxed crystal; Coarse compound phases exist when the content of Ce is up to 0.1%, which is harmful to microstructures of solder alloy and soldering seam. With regard to soldered joints, microstructures formation of the interface between Sn-Ag-Cu-Ce solder and Cu substrate (soldering seam) is different from that of Sn-Ag- Cu-Ce alloy itself, as a result of different cooling speed and dissolution of Cu into solder alloy.