The semiconductive properties of titania are determined by the density of point defects in the crystalline structure. The synthesis method (sol-gel) provides pure and reproducible solids. This technique is very sensitive to hydrolysis catalysts, pH and calcination temperature. In this work, each one of these parameters is systematically varied and correlations with the structures of the obtained solids are established. It is shown that very acidic or basic catalysts are selective to rutile (900 °C). Acid catalysts favour an hydrolysis reaction, but pH does not change the shape or the size of the particles. The reaction mechanism is a nucleophilic substitution SN² in the basic medium and most intermediates in the sol-gel reaction are Ti-OH. The characterization techniques are FTIR, UV-Vis (diffuse reflectance), X-ray diffraction, DTA-TGA and scanning electron microscopy.