Single-walled　carbon　nanotubes　(SWCNTs)　have　been　used　to　prepare　single-layered　graphene　quantum　dots　(GQDs)　through　a　simple　and　green　hydrothermal　etching　method.　After　the　characterization　of　products　and　intermediates　with　scanning　electronic　microscopy,　Raman　and　FTIR,　a　possible　mechanism　has　been　proposed　for　the　formation　of　GQDs.　The　treatment　of　SWCNTs　has　resulted　in　two　kinds　of　GQDs　(i.e.　GQD1　and　GQD2),　both　of　which　are　monodisperse　and　single-layered　nanosheets　with　an　average　lateral　dimension　of　8　nm　and　an　average　height　of　0.5　nm.　Excited　with　365　nm　UV　light,　aqueous　solutions　of　GQDs1　and　GQDs2　give　green　and　yellow　luminescence,　respectively.　The　differences　in　optical　property　between　GQDs1　and　GQDs2　mainly　results　from　their　differences　in　degree　of　oxidation.　(C)　2013　Elsevier　Ltd.　All　rights　reserved.