Cu was loaded on ultrathin HNb3O8 nanosheets via a facile photodeposition method. The oxidation state of the Cu was further verified by XPS. TEM and STEM-EDX mapping demonstrated that the Cu cluster was highly dispersed on the nanosheets. The photocatalytic H-2 evolution activity of (0.5%) Cu/HNb3O8 was about 23.6 times higher than that of the bare HNb3O8 nanosheets under simulated solar light irradiation. The role of Cu in promoting photocatalytic hydrogen evolution activity over HNb3O8 nanosheets was attributed to the reduction of hydrogen evolution potential and the improvement of separation of photogenerated carriers. These results were confirmed by a series of electrochemical characterizations, such as CV, LSV, I-t, and EIS. Finally, photocatalytic hydrogen evolution processes over HNb3O8 nanosheets with and without Cu modification were proposed, which might provide insights into the photocatalytic hydrogen evolution mechanism over niobate-based metal oxides. (C) 2016 Elsevier Inc. All rights reserved.