N,　O-Carboxymethyl　chitosan　(NOCC)　composite　nanofiltration　membranes　having　a　polysulfone　(PSF)　UF　membrane　as　substrate　were　prepared　through　the　method　of　coating　and　cross-linking,　where　glutaraldehyde　was　used　as　the　cross-linker.　The　variance　of　the　streaming　potential　with　the　pressure　was　measured　and　the　result　suggested　that　the　surface　of　the　NOCC/PSF　composite　NF　membrane　acquired　a　negative　surface　charge　distribution　by　adsorption　of　the　anions　from　the　electrolyte　solution.　The　structure　and　surface　of　the　membrane　are　characterized.　Effects　of　the　low-molecular　-weight　organic　additives　into　casting　solution　on　the　rejection　performance　of　the　obtained　membranes　were　investigated.　The　rejections　to　the　electrolyte　solutions　decreased　in　the　order　of　Na2SO4,　NaCl,　MgSO4,　and　MgCl2,　which　is　similar　to　negatively　charged　NF　membranes.