We report the synthesis of TiO2 hierarchical spheres (THS) with large specific surface area via a facile one-pot solvothermal method. The as-prepared THS are self-assembled by ultrathin TiO2 nanosheets with thickness of several nanometers and they show a uniform spherical morphology with an average size of 500-700 nm. However, the as-prepared light yellow THS exhibit inferior photocatalytic activity for hydrogen evolution from water splitting due to the poor crystallization of TiO2 and the existence of oxygen vacancies. Significantly, a subsequent thermal treatment improves the crystallinity of THS, reduces the oxygen vacancies, and thereby enhances the photocatalytic performance. It demonstrates that the sample annealed at 550 degrees C (THS550) exhibits the highest photocatalytic activity, about 5 times higher than that of commercial TiO2 nanoparticles (C-TiO2). Moreover, the THS550 sample loaded with 1 wt% Pt exhibits an hydrogen evolution rate as high as 17.9 mmol h(-1)g(-1), and the corresponding apparent quantum efficiency has been determined to be 28.46% under 350 nm light irradiation. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.