Abstract: The thermomechanical behaviors of the 80Au/20Sn solder at 25, 75, 125 and 200℃ were investigated by constant loading rate/load nanoindentation tests.The results showed that the load-displacement curves depended on the loading rate, applied load and temperature strongly.The loading rate sensitivity, obvious size effect, piling up at 125 and 200℃ were observed.The elastic modulus and hardness were obtained using the Oliver-Pharr method after the contact area was modified based on the semi-ellipse method.The elastic modulus and hardness increase rapidly with the improved loading rate then reach an approximately steady stage, decrease initially as the increased load ultimately attain a steady-state value, decline greatly with the higher temperature.