Abstract: Sn1.0Ag0.5Cu-xAl composite solders were prepared by mechanically mixing method. The effect of nano Al particles on the microstructure and properties of Sn1.0Ag0.5Cu solder were investigated by differnetial scanning calorimetry, STR-1000 micro-joint strength tester and SEM. The results showed that adding nano Al particles does not cause a considerable change in the melting temperature. All samples ranged from 226.9 to 229℃. With the addition of nano Al particles, the wetting angle was decreased and mechanical property was increased. When the addition of nano Al particles was 0.1%, the pull force of solder joint reached the maximum, which was 7.1 N. In addition, the microstructure of Sn1.0Ag0.5Cu-0.1Al solder was significantly refined, and the thickness of interfacial intermetallic compounds (IMC) was effectively inhibited, which may attributed to the adsorption of nanoparticles.