The oxygen plasma-assisted sol-gel method was used to prepare LiMn2O4. The precursor thin film spin-coated on a Pt sheet was treated with oxygen plasma and fired at 723 K. The particle size of LiMn2O4 thin film drastically decreased with the oxygen plasma-assist. Its electrochemical properties were examined by cyclic voltammetry. Two redox peaks (4.00 and 4.15 V vs. Li/Li+) were clearly observed, and oxidation of the electrolyte was suppressed at higher potentials. These results indicate that this method may be promising as a novel route for the preparation of LiMn2O4, which shows high electrochemical performance. (C) 2004 The Electrochemical Society.