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　H2　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.　©　2016　Elsevier　Inc.