Plasmon-induced photoelectrochemistry in the visible region was studied at gold nanoparticle-nanoporous TiO2 composites (Au-TiO2) prepared by photocatalytic deposition of gold in a porous TiO2 film. Photoaction spectra for both the open-circuit potential and short-circuit current were in good agreement with the absorption spectrum of the gold nanoparticles in the TiO2 film. The gold nanoparticles are photoexcited due to plasmon resonance, and charge separation is accomplished by the transfer of photoexcited electrons from the gold particle to the TiO2 conduction band and the simultaneous transfer of compensative electrons from a donor in the solution to the gold particle. Besides its low-cost and facile preparation, a photovoltaic cell with the optimized electron mediator (Fe2+/3+) exhibits an optimum incident photon to current conversion efficiency (IPCE) of 26%. The Au-TiO2 can photocatalytically oxidize ethanol and methanol at the expense of oxygen reduction under visible light; it is potentially applicable to a new class of photocatalysts and photovoltaic fuel cells.