Large-surface-area mesoporous Nb2O5 microspheres were successfully grown in-situ on the surface of g-C3N4 nanosheets via a facile solvothermal process with the aid of Pluronic P123 as a structure-directing agent. The resultant g-C3N4/Nb2O5 nanocomposites exhibited enhanced photocatalytic activity for H-2 evolution from water splitting under visible light irradiation as compared to pure g-C3N4. The optimal composite with 38.1 wt% Nb2O5 showed a hydrogen evolution rate of 1710.04 mu mol h(-1) g(-1), which is 4.7 times higher than that of pure g-C3N4. The enhanced photocatalytic activity could be attributed to the sufficient contact interface in the heterostructure and large specific surface area, which leads to effective charge separation between g-C3N4 and Nb2O5. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.