Effects of carboxylic acids with different molecular structures on the microstructure and performance of nano-crystalline titania have been investigated. It was found that autoclaving TiCl4 aqueous solution in the presence of acetic acid led to the formation of rod-like titania with pure rutile phase, whereas in the case of tartaric acid, citric acid, propylenedi-aminetetraacetic acid or lysine, pure anatase titania with different microstructure was obtained. The change of the phase composition, crystal size and microstructure of titania should be contributed to the coordinating effects of carboxylic acids with titanium ions and their adsorption on the surface of titania nanoparticles. The investigation on photocatalytic activity suggested that rutile titania prepared exhibited a poor photocatalytic activity for the degradation of methyl orange, but a relative high activity for the degradation of rhodamine B. Compared with P25, anatase titania prepared in the presence of citric acid or L-lysine demonstrated high photocatalytic activity for the degradation of methyl orange and rhodamine B. (C) 2007 Elsevier B.V. All rights reserved.