The electrochemical hydriding/dehydriding under galvanostatic conditions of nanostructured Mg2-x Sn (x) Ni (x = 0,0.1,0.3) were studied at different temperatures in the range 28-45 degrees C. The discharge capacity, cycle life and electrochemical impedance of the alloys were found to depend on the presence of Sn. Tin decreases the maximum electrochemical capacity, but essentially improves the cycle life of Mg2Ni. Intensive corrosion of surface Mg was found to take place during the first 2-3 charge/discharge cycles to a much larger extent for Mg2Ni, compared to the tin containing alloys. Sn decreases the electron density around the Mg atoms and therefore impedes magnesium oxidation. It was also found that Sn hampers charge transfer but reduces the hydrogen diffusion resistance in Mg2Ni based alloys.