Visible　light-activated　SnNb　2O　6　nanosheets　(NSs)　with　high　surface　area　and　small　crystallites　have　been　prepared　by　a　microwave-assisted　template-free　hydrothermal　method　without　exfoliation　for　the　first　time.　This　approach　could　be　used　to　prepare　the　functional　materials　efficiently　and　extended　to　synthesizing　two-dimensional　nanosheet　materials　directly　as　well.　The　crystalline　phases,　photoabsorption　performances,　and　surface　areas　and　porosity　of　the　samples　are　characterized　by　XRD,　UV-vis　diffuse　reflectance　spectroscopy　(UV-vis　DRS),　and　N　2-adsorption.　Results　show　that　a　hypsochromic　shift　of　the　photoabsorption　edge　is　observed,　which　reflects　an　obvious　quantum　size　effect.　TEM　images　reveal　SnNb　2O　6　nanosheets　with　a　thickness　of　1-4　nm　versus　several　hundred　nanometres　in　lateral　size.　Based　on　the　experimental　results,　the　formation　mechanism　of　SnNb　2O　6　nanosheets　is　also　studied　and　proposed,　which　reasonably　follows　a　synergy　interaction　of　reaction-crystallization　and　dissolution-recrystallization　processes.　Due　to　the　unique　morphology,　larger　surface　area,　smaller　crystallites　and　stronger　redox　ability　of　the　photogenerated　hole-electron　pair,　these　photocatalysts　show　much　higher　photocatalytic　activities　for　the　degradation　of　rhodamine　B　(RhB)　compared　with　their　counterparts　prepared　by　the　traditional　solid-state　reaction.　The　reaction　rate　is　enhanced　by　over　4　times　and　the　RhB　molecule　can　be　mineralized　into　CO　2　and　H　2O　over　SnNb　2O　6　NSs.　The　decomposition　mechanism　of　RhB　over　SnNb　2O　6　under　visible　light　irradiation　and　the　active　species　in　the　photocatalytic　process　have　also　been　discussed.　©　2012　The　Royal　Society　of　Chemistry.