Abstract: The newly developed lead-free solders should have good mechanical properties，as well as excellent creep resistance in order to meet the needs of reliability required by electronic industries. Nano-sized polyhedral oligomeric silsesquioxane (POSS) reinforcement particles were incorporated into the promising lead-free solder，Sn-3. 5Ag，to improve the mechanical property of the lead-free solder. Experimental results show that the thickness of intermetallic compound (IMC) layer between solder and substrate Cu is restrained when the mass fraction of POSS is less than 2%. The composite solders contain different POSS reinforcement types and mass fractions，and their joints possess better mechanical properties. The creep rupture lives are enhanced in the composite solder joint at different temperatures and different stress combinations compared to the Sn-3.5Ag solder joint，especially at low temperatures.