In this paper, N-doped mesoporous-assembled TiO(2) and N-doped non-mesoporous-assembled commercial TiO(2) (Degussa P-25) nanocrystals were comparatively investigated for photocatalytic H(2) production from water splitting under visible light irradiation. The mesoporous-assembled TiO(2) photocatalyst with nanocrystalline and narrow monomodal pore size distribution characteristics was synthesized by a sol-gel process with the aid of structure-directing surfactant under mild conditions. The N-doping technique was directly performed by calcining the mixture of the TiO(2) photocatalysts and urea, as a N source, at different N contents and calcination temperatures. All prepared photocatalysts were systematically characterized by N(2) adsorption-desorption, Brunauer-Emmett-Teller (BET) surface area analysis, Barrett-joyner-Halenda (BJH) pore size distribution analysis, UV-visible spectroscopy, X-ray diffraction (XRD), and X-ray photoelectron microscopy (XPS). From the experimental results, it was found that N-doped mesoporous-assembled TiO(2) prepared at a urea:TiO(2) molar ratio of 1:1 and a calcination temperature of 250 degrees C exhibited relatively high photocatalytic activity toward hydrogen production. For the N-doped commercial TiO(2), the preparation conditions of a molar ratio of 0.5:1 and a temperature of 250 degrees C showed the best photocatalytic activity, but was still less photocatalytic ally active than N-doped mesoporous-assembled TiO(2) prepared at the optimum conditions. The results indicated the importance of the mesoporous characteristic of the photocatalyst in enhancing the photocatalytic activity by increasing the specific surface area and N-doping capability. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.