Nanosized biphase titania photocatalysts with various phase compositions were synthesized by hydrothermal method. Gas-phase photocatalytic oxidations of hexane and methanol were investigated in the presence of the biphase titania catalysts. A clear synergetic effect between the anatase and rutile phases was observed for the two reactions. Mechanical mixtures of the two titania phases were also prepared to investigate this synergetic effect. It was found that the closer the anatase and rutile particles are in contact, the more evident the synergetic effect is. The result of a long-term experiment shows that the activity of the synthesized biphase catalyst is very stable. Sulfation of these biphase catalysts does not improve their activity and stability as that of the single phase anatase TiO2 catalyst. (C) 2004 Elsevier B.V. All rights reserved.