Abstract: Rare earth (RE) elements and low melting-point Ga elements are often added as alloying elements to lead-free solders to improve the overall performance and reliability of the solder. When RE and Ga elements are added in combination, their synergistic effects can further improve the microstructure and properties of the solder. In particular, Ga element can effectively inhibit the growth of Sn whiskers in lead-free solders containing RE Nd. Therefore, this article reviewed the effects of RE, low melting-point Ga element and their synergistic effects on the microstructure, wettability, melting characteristics, mechanical properties and reliability of lead-free solders. What’s more, the mechanism of Sn whiskers formation in lead-free solders bearing RE and the factors affecting the growth of Sn whiskers were introduced. Finally, the deficiencies in the research of lead-free solder containing RE and Ga elements were summarized, and the future research direction was looked-ahead.