Cu/Sn alloy electrode, as an anode for Li ion secondary batteries, was fabricated by annealing of Sn thin film electroplated on copper thin foil. The structure of Cu/Sn alloy electrode was determined using XRD, SEM and TEM. The thin film was consisted of Cu6Sn5, Cu3Sn and so on, the major component was a few ten nanometer sized Cu6Sn5 grains and the minor (Cu3Sn and β-(Cu,Sn)) was dispersed among the Cu6Sn5 grains. The electrochemical properties of Cu6Sn5 thin film were evaluated in coin type half-cell, which was configured with Cu6Sn5, thin film electrode, Li metal electrode and typical 1 mol LiPF6 in EC:DMC (1:1) electrolyte. Annealed Cu/Sn electrode took and released Li ions well during Li insertion and de-insertion. Cycle performance of annealed Cu/Sn electrode was better than that of as-deposited Sn electrode, which was caused by topotactic reaction of Cu6Sn5and composite structure of Cu/Sn alloys.