ABSTRCT: The intermetallic compound Cu3Sn and Cu6Sn5 which generated in lead-free solder Sn3.0Ag0.5Cu were studied and characterised by nanoindentation. The strain-rate is 0.01 s-1, 0.05s-1, 0.25s-1, 0.5s-1 respectively. The strain-rate effect on mechanical properties of Cu3Sn and Cu6Sn5 were studied. The mechanical responses of both Cu6Sn5 and Cu3Sn (IMCs) show large dependence on the strain rate during loading. In addition, multiple pop-in events are observed in Cu6Sn5 but not evident in Cu3Sn. During loading, the contact stiffness of IMCs increases almost linearly with the indentation depth under each strain rate. In total, the hardness and elastic modulus of Cu3Sn are larger than those of Cu6Sn5, and the hardness of both Cu6Sn5 and Cu3Sn increase with increasing strain rate. During the holding stage, creep deformations of IMCs increase as loading strain rate increases. During the holding stage, creep displacement increases with the increasing strain rate during loading. The creep strain rate sensitivity index m of Cu, Cu3Sn , Cu6Sn5 and solder are 0.01627、0.0117、0.0184 and 0.0661 respectively when the strain-rate is 0.05s-1.