Abstract: Sn-based solder is a widely used interconnection material in the field of electronic packaging; however, the performance requirements for these solders are becoming increasingly demanding owing to the rapid development in this area. In recent years, the addition of micro/nanoreinforcement phases to Sn-based solders has provided a solution to improve the intrinsic properties of the solders. This paper reviews the progress in Sn-based micro/nanoreinforced composite solders over the past decade. The types of reinforcement particles, preparation methods of the composite solders, and strengthening effects on the microstructure, wettability, melting point, mechanical properties, and corrosion resistance under different particle-addition levels are discussed and summarized. The mechanisms of performance enhancement are summarized based on material-strengthening effects such as grain refinement and second-phase dispersion strengthening. In addition, we discuss the current shortcomings of such composite solders and possible future improvements, thereby establishing a theoretical foundation for the future development of Sn-based solders.