Well-defined spherical mesoporous TiO2 was prepared from a poly(ethylene glycol)-poly(propylene glycol)-based triblock copolymer and titanium isopropoxide mixed with 2,4-pentanedione by using a simple sol-gel approach in aqueous solution. Hydrothermal treatment was performed to increase the crystallinity, thermal stability, surface area, and photocatalytic activity of the mesoporous TiO2. The hydrothermally treated mesoporous TiO2 materials were found to have a high crystallinity with a nanocrystalline anatase structure even in the as-synthesized state, whereas untreated materials were found to have an amorphous or semicrystalline phase prior to calcination at 300 degrees C. The surface area of hydrothermally treated mesoporous TiO2 was found to exceed 395 m(2) g(-1), whereas the areas of the untreated materials were less than 123 m(2) g(-1). The pore size distributions of the hydrothermally treated mesoporous TiO2 materials were found to be narrower than those of untreated materials; the average pore size increased from 5.7 to 10.1 nm with increases in the calcination temperature. The photocatalytic activity of hydrothermally treated mesoporous TiO2 is significantly higher than the activities of untreated materials, with a maximum decomposition rate that is three times faster than that of a commercial TiO2, P25. The high photocatalytic activity of mesoporous TiO2 is due to the large surface area and high crystallinity with a nanocrystalline anatase that is induced by the hydrothermal treatment. (C) 2007 Elsevier B.V All rights reserved.