Several thin film composite nanofiltration membranes have been prepared by spin coating a sulfonated poly(ether ether ketone) solution on a polyethersulfone support, followed by thermal treatment. The most optimal developed nanofiltration membrane shows a clean water permeance of similar to 4.5 L m(-2) h(-1) bar(-1) and a molecular weight cut off (MWCO) of similar to 500 g mol(-1). No irreversible changes in membrane performance have been observed after prolonged exposure (up to several weeks) of this membrane to solutions with a pH in the range 0-14. Compared to Desal-5-DK, the developed membrane displays a similar water permeance and a higher NaCl retention. In comparison to commercially available pH stable membranes, MPF-34 and NP030P, it reveals a higher water permeance. Permeance and MWCO analysis at varying pH indicates that charge effects induce reversible changes in the membrane materials properties. Especially at strongly alkaline conditions the developed membrane appears to be more open. (C) 2011 Elsevier B.V. All rights reserved.