Monolayer　SnNb2O6　two-dimensional　(2D)　nanosheets　with　high　crystallinity　are　prepared　by　an　one-pot　and　eco-friendly　hydrothermal　method　without　any　organic　additives.　For　the　first　time,　these　SnNb2O6　nanosheets　are　applied　to　the　photocatalytic　reduction　of　CO2　with　H2O　to　CH4　in　the　absence　of　co-catalysts　and　sacrificial　agents　under　visible　light　irradiation.　The　structural　features,　morphology,　photo-absorption　performance,　and　photoelectric　response　have　been　investigated　in　detail.　Results　show　the　as-prepared　SnNb2O6　samples　with　typical　2D　nanosheets　in　the　thickness　of　about　1　nm.　Owing　to　the　unique　features　of　the　nanosheets,　the　surface　area,　photoelectrical　properties　and　the　surface　basicity　of　SnNb2O6　are　greatly　improved　compared　with　the　counterpart　prepared　by　traditional　solid　state　reaction.　Furthermore,　the　adsorption　capacity　of　CO2　on　SnNb2O6　nanosheets　is　much　higher　than　that　of　layered　SnNb2O6.　Thus,　the　photocatalytic　activity　of　SnNb2O6　nanosheets　for　the　reduction　of　CO2　is　about　45　and　4　times　higher　than　those　of　the　references　(layered　SnNb2O6　and　common　N-doped　TiO2),　respectively.　To　understand　the　interactions　between　the　CO2　molecule　and　the　surface　of　the　photocatalyst,　and　the　reactive　species　in　the　reduction　process,　the　intermediates　have　also　been　detected　by　in　situ　FTIR　with　and　without　visible　light　irradiation.　Finally,　a　possible　mechanism　for　the　photocatalytic　reduction　of　CO2　with　H2O　to　CH4　on　SnNb2O6　nanosheets　is　proposed.　We　believe　this　work　will　provide　new　opportunities　for　expanding　the　family　of　visible-light　driven　photocatalysts　for　the　reduction　of　CO2.