A facile method for obtaining highly photoactive bi-phase TiO2 photocatalyst with a small crystalline size and very large specific surface area was developed. This was simply done by hydrolysis of titanium tetraisopropoxide (TTIP) in pure water at 70 degrees C and followed by drying at 100 degrees C. The prepared TiO2 powder samples were characterized with X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and BET surface areas. The photocatalytic activity was evaluated by the photocatalytic oxidation of acetone in air. The results showed that the photocatalytic activity of the prepared TiO2 powder slightly exceeded that of Degussa P25. This might be attributed to the fact that the prepared TiO2 powder had a very large specific surface area (750 m(2) g(-1)) and small crystallite size (about 5 nm), but relative low crystallinity, comparing with Degussa P25 photocatalyst. (c) 2005 Elsevier B.V. All rights reserved.