Anatase TiO2 sols were synthesized Under mild conditions (i.e. 75 degreesC and ambient pressure) by hydrolysis of titanium-n-butoxide in abundant acidic aqueous solution and subsequent reflux to enhance crystallization. The influences of various acidities on crystallinity, morphology, and size of the obtained TiO2 sol particles were investigated. At room temperature and in ambient atmosphere, crystalline TiO2 thin films were deposited on quartz glass slides from the as-prepared TiO2 sol by a dip-coating method. TiO2 films on substrates could be thickened by means of consecutive dipcoating processes. The photocatalytic activities of the TiO2 thin films were assessed by the degradation of X-3B in aqueous solution under aerated conditions. The preparation process of photocatalytic TiO2 thin films was quite simple and a low-temperature route. (C) 2004 Elsevier B.V. All rights reserved.