Crystalline BaTiO3 nanoparticles were prepared in solution at low reaction temperature. The formation of crystalline BaTiO3 and its crystallite size was strongly dependent on the concentration of the OH- ion, total concentration of the reactants, reaction temperature and reaction time. The formation pathway and the variation of crystallite size were understood by several model experiments using NaOH as the additional source of OH- ions. At higher OH- concentrations, the crystallite size of BaTiO3 was found to be decreased with increasing OH- concentrations, while it was increased with increasing reactant concentrations. (C) 2006 F blished by Elsevier Ltd.