SnO x thin films were prepared by reactive radio frequency magnetron sputtering with different sputtering powers. X-ray photoelectron spectroscopy suggested that all the films have similar chemical stoichiometry as SnO1.5. X-ray diffraction and transmission electro microscopy results showed that crystal size of the SnO x thin films gradually increases with increase of sputtering power from 50 to 150W. Cyclic voltammetry and galvanostatic charge/discharge cycling measurements indicated that the electrochemical properties of SnO x films strongly rely on their crystal sizes as well as surface morphologies. The SnO x film deposited at sputtering power of 120W exhibits the best electrochemical performances. It could deliver a reversible capacity of 670μAhcm−2 μm−1 at 50μAcm−2 in the voltage range of 0.1–1.2V up to 50 cycles.