Water-soluble　graphene　sheet　was　prepared　via　chemical　reduction　of　graphene　oxide　(GO)　in　the　presence　of　polyacetylene　bearing　a　quaternary　ammonium　pendant　(Pac),　with　a　relatively　low　feed　ratio　of　1/3　(Pac/GO,　w/w).　The　non-covalent　functionalization　of　graphene　by　Pac　was　mainly　based　on　the　electrostatic　attraction　and　π-π　interaction,　the　resultant　material　G-Pac　showed　good　solubility　in　water　with　the　concentration　of　0.28　mg　mL　-1.　In　virtue　of　the　unique　sp2-conjugated　structure　of　graphene,　it　displayed　a　prominent　optical　limiting　response,　which　could　be　potentially　used　in　photonic　or　optoelectronic　devices　to　protect　human　eyes　or　optical　sensors　from　damage　by　intense　laser　irradiation.　©　2012　The　Royal　Society　of　Chemistry.