Fungus-like　potassium　niobate　(KNb3O8)　nanosheets　have　been　synthesized　on　indium-doped　tin　oxide　(ITO)　glass　substrates　by　a　simple　and　environmental　friendly　two-step　hydrothermal　process.　The　prepared　samples　have　been　characterized　by　using　X-ray　Diffraction　(XRD),　Field　Emission　Scanning　Electron　Microscope　(FESEM),　High　Resolution　Transmission　Electron　Microscope　(HRTEM),　Fourier　Transform　Infra-Red　Spectroscopy　(FTIR),　Raman　Spectroscopy　and　X-ray　Photoelectron　Spectroscopy　(XPS).　Furthermore,　the　photoluminescence　(PL)　of　KNb3O8　nanosheets　have　been　systematically　studied.　The　results　showed　that　the　PL　spectrum　is　between　300　and　645　nm　with　a　325　nm　light　excitation,　which　is　divided　into　some　sub-peaks.　It　is　different　from　the　perfect　KNb3O8　nanosheets　whose　PL　emission　peaks　located　at　near　433　nm.　It　should　be　originated　from　the　effect　of　the　oxygen　(O)　vacancies　in　the　KNb3O8　nanosheets,　which　the　PLs　peaks　can　be　found　at　about　490　nm　and　530　nm　by　different　position　of　O　vacancy.　The　experimental　results　are　in　accordance　with　the　first-principles　calculations.　Our　results　may　present　a　feasible　clue　to　estimate　the　defect　position　in　KNb3O8　by　the　shape　analysis　of　its　spectrum　of　PLs.　(C)　2017　Elsevier　B.V.　All　rights　reserved.