A synthetic strategy for magnetite (Fe3O4) crystallite size control is reported, along with the detailed characterization and electrochemical measurements of Fe3O4 samples of varying crystallite sizes. Nanocrystalline Fe3O4 is prepared by coprecipitation induced by triethylamine from aqueous iron(II) and iron(III) chloride solutions of varying concentrations. Variation of the iron(II) and iron(III) concentrations results in crystallite size control of the Fe3O4 products. Materials characterization of the Fe3O4 samples is reported, including X-ray diffraction, transmission electron microscopy, particle size, and saturation magnetization results. A strong correlation between discharge capacity and voltage recovery behavior vs magnetite crystallite size was observed when tested as an electrode material in lithium electrochemical cells. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3478667] All rights reserved.