Nanosized pure TiO2 particles with high crystallinity and large surface area were prepared by hydrolysis of tetrabutyl titanate in water/Triton X-100/isooctane reverse micelle solutions as reaction media followed by hydrothermal treatment to improve crystallinity. The prepared TiO2 nanoparticles were characterized by XRD, BET, TGA, FT-IR and TEM. The size of ultrafine particles was controlled by changing the water content of the reverse micelle solution. The TiO2 particles showed monodispersity, large surface area and high degrees of crystallinity and thermostability. The photocatalytic activity of the TiO2 particles was evaluated by decomposition of toluene in the gas phase. The activity of the TiO2 nanoparticles was higher than that of commercially available anatase fine particles, such as ST-01, which is one of the most active photocatalysts for degradation of organic compounds in the gas phase. (c) 2006 Elsevier B.V. All rights reserved.