HCl concentration and reaction time are the decisive factors in determining the structure of precipitates in the process of synthesis of TiO 2 particles from aqueous TiOCl 2 solution by precipitation and the volumetric proportion of brookite phase in TiO 2 particles can be controlled by these two factors. As reaction rate increases with increase of reaction temperature, the reaction time, at which maximum volumetric proportion of brookite phase in TiO 2 particles was obtained, was reduced. The brookite was transformed directly to rutile phase with only increase of reaction time. And precipitation was delayed with increase of HCl concentration because the amount of H 2 O, which is necessary source of oxygen for conversion of Ti +4 to TiO 2 , was relatively reduced with increase of that. Brookite in the mixture phase powder was finally transformed to rutile phase via anatase through heat-treatment.