TiO2 nanoparticles were produced by controlled hydrolysis of TTIP in the W/C microemulsions stabilized by polymeric surfactants. The prepared particles were characterized using TGA-DTA, FT-IR, XRD, SEM and TEM. It was found that the residual hydroxyl group and the organic compounds were completely removed by calcination at 350degreesC and the amorphous phase transformed to an anatase structure above 420degreesC, though the particles dried at 105degreesC without calcination were amorphous. The crystallite size could be controlled by the water-to-surfactant mole ratio, W-0, and the particle size increases from 8 to 18 nm with an increase of the 970 ratio. In addition, the photocatalytic activity decreases with an increase of the W-0 ratio, though still higher than that of normal bulk TiO2. (C) 2003 Elsevier B.V. All rights reserved.