Graphene modified semiconductor photocatalysts (GMSP) have attracted extensive attention due to their great photoactivities and promising prospect in environmental area. Although several GMSP samples have been prepared, the photocatalytic mechanism of these composites under visible-light illumination is still misty. Based on their energy band structures, electron transport model of graphene/titanate nanotubes (TNTs) photocatalyst under visible-light illumination is proposed in this study. Graphene and TNTs make a metal-semiconductor junction, and graphene can play as a sensitizer to endow the photocatalyst with an excellent visible-light response. Quantum tunneling is the major way to achieve the electron transport between graphene and TNTs, and the tunneling probability was calculated in the theory. Moreover, by using scanning tunneling microscope, electron paramagnetic resonance and photoluminescence spectra, the electron transport from graphene to TNTs under visible-light irradiation is confirmed unambiguously. (C) 2012 Elsevier B.V. All rights reserved.