The effect of nano-particles TiO2 on the microstructures and properties of SnAgCu solders was investigated. The results indicate that adding a small amount of nano-particles TiO2 can improve the wettability of SnAgCu solders, and the mechanical properties of solder joints can be enhanced significantly; however, excessive nano-particles would reduce the properties. It can be found that the optimum content of nano-particles is 0.1 wt% for SnAgCu solders, when the matrix microstructure of solders may be refined obviously, and the dendrite-arm spacing of SnAgCu solders is decreased by 62.5% after soldering. Moreover, during thermal cycling tests, the SnAgCu solder joints show superior thermal fatigue resistance with the addition of 0.1wt% TiO2 because the particles restrict the movement of dislocations, thus hindering the propagation of cracks in matrix microstructure.