Nanowires have attracted increasing interests because one-dimensional (1-D) nanomaterials can offer a range of unique advantages in many energy related fields.[1-6] For previous Iithium battery applications, bulk materials made of nanowires were usually used as the electrodes.Although the electrochemical properties could be improved, the fast capacity fading is still one of the key issues and the intrinsic reasons are not clear until now.In situ probing has been increasingly employed in nanotechnology.[7-8] To understand intrinsic reason of capacity fading,we designed the single nanowire electrochemical devices for in situ probing the direct relationship between electrical transport, structure, and electrochemical properties of the single nanowire electrode, which may push the fundamental limits of the nanowire materials for energy storage applications.[9] Our results show that conductivity of the nanowire electrode decreased during theelectrochemical reaction, which limits the cycle life of the devices.