Cu nanowires with diameter of about 50 nm were electrochemically deposited in anodic alumina mem-brane.An in-situ high-temperature XRD technique was used to measure the crystalline structures.The results demon-strate that these Cu nanowires have a thermal expansion coefficient of about 2.6×10-5 K-1

which is a little larger than the bulk’s one.These polycrystalline Cu nanowires are completely different from the zero-expansion Cu nanowires reported in previous reference.It is concluded that the thermal expansion coefficient is dependent on the crystalline perfection in nanowires.