Abstract: The effect of Nb nano-particles on the microstructures and mechanical properties of Sn-0.7Cu composite solder was studied in this paper.The results showed that the microstructure of Sn-0.7Cu composite solder was refined by adding Nb nano-particles and the tensile strength of joint with Sn-0.7Cu composite solder was improved.When Nb content was 0.12%（mass fraction）,the maximum tensile strength reached 25.36 MPa,but the elongation of the solder was reduced.The fracture mode of Sn-0.7Cu-xNb composite solder was all plastic fracture.The size of dimples on the fracture surface of Sn-0.7Cu composite solder decreased gradually with the increase of Nb content,which indicated that the growth of Cu₆Sn₅ intermetallic was inhibited by adding a small amount of Nb nano-particles.