The mesoporous Au-TiO2 nanocomposites with different Au concentrations were prepared via a co-polymer assisted so-gel method. The structures have been characterized by powder X-Ray diffraction, N-2 adsorption-desorption isotherms, diffuse reflectance UV-Vis spectroscopy, X-ray photoemission spectroscopy, transmission electron microscopy. Most generated Au nanoparticles were embedded in the mesoporous TiO2 matrix. The prepared Au-TiO2 nanocomposites exhibit remarkable visible-light activity for H-2 evolution from photocatalytic water reduction in the presence of ascorbic acid as the electron donor. By comparing with Pt-TiO2 samples, we found that the visible-light activity of the Au-TiO2 nanocomposites could be partially contributed by the defects/impurity states in the TiO2 matrix, while the gold surface plasmons could significantly enhance the weak visible-light excitation of TiO2 matrix. In addition, further studies by controlling irradiation wavelengths suggest that some plasmon-excited electrons could transfer from Au nanoparticles to the contacting TiO2 to reduce water for H-2 generation. We believe that these Au-TiO2 nanocomposites as well as the mechanistic studies would have considerable impact on future development of metal-semiconductor hybrid photocatalysts for efficient solar hydrogen production. Copyright (c) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.