Bimodal mesoporous TiO2 microspheres with high photocatalytic activity were prepared by a hydrothermal method using titanium sulfate as precursor in the presence of urea. The results indicate that all prepared samples show bimodal pore-size distributions in the mesoporous region: smaller intraaggregated pores with peak pore diameter of ca. 2 nm and larger inter-aggregated pores with peak pore diameter of ca. 12.5 nm. The molar ratio of urea to Ti(SO4)(2) (R-u) has an obvious influence on the morphology, microstructure and photocatalytic activity of TiO2. With increasing R-u, specific surface areas and porosity increase, contrarily, the crystallite size and relative anatase crystallinity decrease. The photocatalytic activity first increases with R-u. At R-u = 2.0, the photocatalytic activity reaches the highest and is obviously higher than that of Degussa P25. With further increasing R-u, the photocatalytic activity decreases. The formation rate of hydroxyl radicals during photocatalysis has a positive correlation with the photocatalytic activity. (C) 2009 Elsevier B.V. All rights reserved.