Sulfonated poly(ether ether ketone)s (SPEEKs) with different sulfonation degrees (DS) were synthesized and characterized using FTIR and NMR for the preparation of blend nanofiltration (NF) membranes. Blends of polyethersulfone and SPEEK at various SPEEK concentrations and various DS were prepared by a simple dry-jet wet spinning technique. The changes in the morphological and electrical properties of the blend membranes were deduced by employing the combination of irreversible thermodynamic model, Steric-Hindrance Pore (SHP) model and Teorell-Meyer-Sievers (TMS) model and the modeling results have been analyzed and discussed in detail. The results showed that the membrane water flux, pore size and surface charge were dependent on the content and DS of SPEEK used. FESEM-EDX results also provided supporting evidence for the trends observed for the morphological and electrical studies. (C) 2009 Elsevier B.V. All rights reserved.