In this work, the mesoporous-assembled Nb2O5 nanoparticles synthesized via a modified sol-gel method with the aid of a mesopore-directing surfactant were thermally treated under various calcination temperatures. The effect of thermal treatment on their physicochemical properties and photocatalytic hydrogen production activity under UV light irradiation was systematically studied. The synthesized Nb2O5 nanoparticles were characterized by X-ray diffraction, N-2 adsorption-desorption, UV-visible absorbance spectroscopy, scanning electron microscopy, transmission electron microscopy, and selected-area electron diffraction analyses. The experimental results clearly revealed that the optimization of calcination temperature was required in order to achieve the synthesized Nb2O5 nanoparticle with the most suitable physicochemical properties and the highest photocatalytic activity. A maximum hydrogen production rate was obtained with the synthesized Nb2O5 nanoparticle calcined at the optimum temperature of 550 degrees C, exhibiting an acceptably high level as compared with the hydrogen production rate of the commercial P-25 TiO2 powder under identical reaction conditions. (C) 2012 Elsevier B.V. All rights reserved.