SnP x O y thin films were deposited on stainless steel substrates by electron-beam evaporation for use as anodes in thin-film lithium ion batteries. The thin films were heat-treated at various temperatures for 4h, and their composition, microstructure, and electrochemical properties were characterized by Rutherford backscattering spectroscopy (RBS), X-ray diffraction (XRD), cyclic voltammetry (CV), and AC impedance spectroscopy. The specific discharge capacity of the as-deposited SnP x O y thin film anode decreased rapidly to 12μAhcm−2-μm within 10 cycles. However, after heat treatment for 4h at 500°C, it maintained a high specific discharge capacity of 136μAhcm−2-μm and excellent cyclability even after 300 cycles, in contrast to pure SnO x thin film.