A novel nanofiltration membrane was prepared and applied for the rejection of dye and divalent salt and for the separation between dye and NaCl. The membrane was obtained by two steps: At first chloromethylated poly(phthalazinone ether sulfone ketone) (CMPPESK) was prepared into the membrane by a phase inversion method, and then CMPPESK membrane was immersed into an aqueous trimethylamine solution to induct quaternary nitrogen groups into the membrane. The resulting membrane owns positive charges and is called quaternized PPESK (QAPPESK) NF membrane. Compared with CMPPESK membranes, QAPPESK membranes have dramatic increase in the pure water flux and the rejection of dyes and MgCl2. The factors affecting the membrane properties were investigated, such as evaporation time, coagulation temperature and additives, as well as quaternization conditions including trimethylamine concentration, quaternization time and quaternization temperature. The results show QAPPESK membrane with polyethyleneglycol 400 (PEG400) as additive has perfect properties for the removal of dyes and the separation between dyes and NaCl, and the highest permeation flux is about 193 kg/m(2) h at 0.25 MPa, and the membrane with ethyleneglycol monomethylether (EGME) as additive is more suitable for the rejection of MgCl2. The flux increases significantly with the increase of trimethylamine concentration, quaternization temperature and quaternization time. Furthermore, QAPPESK membranes were pretreated or posttreated by boiling in water or heating at 80degreesC in the air. It is found that the two methods are effective for increasing the rejection of MgCl2. The chemical stability of QAPPESK membranes was also investigated. The results indicate that they have excellent acid resistance and oxide resistance. (C) 2004 Elsevier B.V. All rights reserved.