The electrochemical properties of nanocomposite Cr2O3-InP thin film prepared by the pulsed laser deposition method have been investigated by cyclic voltammetry and charge/discharge measurements. The large reversible capacity of the nanocomposite Cr2O3-InP thin film was 653 mAh/g. A couple of reduction and oxidation peaks at 1.45 and 1.14-2.6 V were observed from the cyclic voltammogram. The electrochemical reaction mechanisms of Cr2O3-InP with lithium were examined by X-ray photoelectron spectroscopy, high resolution transmission electron microscopy, and selected area electron diffraction. An interesting anion exchange phenomenon was observed, wherein CrP instead of the original Cr2O3 was formed as the charging product associated with the decomposition of Li3P rather than Li2O. The reversible alloying/dealloying of In with Li and the reversible formation and decomposition of CrP were involved in subsequent cycles. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3446825] All rights reserved.