Different particle size and stability of TiO2 colloids, using acetylacetone modified titanium isopropoxide as precursor, have been synthesized under various polarity organic solvent. In this study, the chelating bond between titanium isopropoxide and acetylacetone was examined by FTIR. The crystalline structure of TiO2 colloid prepared by using acetylacetone modified or un-modified titanium isopropoxide as precursor were determined by X-ray diffraction, before or after sintering process. The TiO2 colloidal size and aggregation phenomenon were obtained from light scattering and photographs of SEM and TEM. From the observation of experiments, stable TiO2 colloid could not be obtained if the hydrolysis/condensation reaction rate of titanium precursor was not inhibited by acetylacetone. The solvent effect on the colloidal particle size and stability were explained by Hansen solubility parameters. In this study, the Hansen solubility parameters of acetylacetone modified TiO, were estimated, which would be useful information in the preparation of stable TiO, colloid. (c) 2006 Elsevier B.V. All rights reserved.