Novel graphene-TiO2 (GR-TiO2) composite photocatalysts were synthesized by hydrothermal method. During the hydrothermal process, both the reduction of graphene oxide and loading of TiO2 nanoparticles on graphene were achieved. The structure, surface morphology, chemical composition and optical properties of composites were studied using XRD, TEM, XPS, DRS and PL spectroscopy. The absorption edge of TiO2 shifted to visible-light region with increasing amount of graphene in the composite samples. The photocatalytic degradation of methyl orange (MO) was carried out using graphene-TiO2 composite catalysts in order to study the photocatalytic efficiency. The results showed that GR-TiO2 composites can efficiently photodegrade MO, showing an enhanced photocatalytic activity over pure TiO2 under visible-light irradiation. The enhanced photocatalytic activity of the composite catalysts might be attributed to great adsorptivity of dyes, extended light absorption range and efficient charge separation due to giant pi-conjugation system and two-dimensional planar structure of graphene. (C) 2012 Elsevier B.V. All rights reserved.