Highly active TiO2/V-TiO2 composite photocatalysts with an n-n heterojunction semiconductor structure have been prepared by mixing TiO2 sol with sol-gel derived V-TiO2 powders that have adsorbed ammonium oleate in advance, followed by drying and calcination. These composite photocatalysts were characterized by XRD, TEM, BET, XPS, UV-vis and PL spectroscopy. The photodegradation of methyl orange in aqueous solution under UV-vis light irradiation has been investigated over TiO2-based photocatalysts consisting of different TiO2/V-TiO2 ratios and different vanadium contents. TiO2/V-TiO2 composite photocatalysts were generally shown to have a much higher photocatalytic destruction rate than that of undoped TiO2, which is ascribed mainly to the electrostatic-field-driven electron-hole separation in TiO2/V-TiO2 composite photocatalysts. The best TiO2/V-TiO2 composite with the mass ratio of TiO2:0.5 at.%V-TiO2 equal to 12:1 demonstrates 5.9 times the photocatalytic activity of that of undoped TiO2 with comparable crystallite size and specific surface area. The effect of photocatalysts composition on the photoactivity was discussed. (C) 2010 Elsevier B.V. All rights reserved.