TiO2 thin films were deposited on Si(100) and steel substrates by Pyrosol technique. The layer morphology depends on the concentration of titanium tetra-isopropoxide (TTIP) used as molecular precursor in solutions with acetylacetone (Acac). The concentration and, as a result, the viscosity of these TTIP/Acac starting solutions plays an important role on the efficiency of their nebulization and, consequently, on the microstructure and the growth kinetics of the TiO2 thin films. The correlations between the composition of the TTIP/Acac solutions and the structure, the morphology, optical properties and the deposition rate of the films are presented and discussed. Growth rates as high as 1.8 mu m/min are obtained using pure TTIP without Acac solvent. The photocatalytic activity of these Pyrosol TiO2 thin films grown using TTIP with and without Acac solvent has been investigated and a negative effect of the solvent was found. (C) 2007 Elsevier B.V. All rights reserved.