In this study, the surface charged and structural information of sulfonated polyethersulfone nanofiltration membrane are acquired through the analysis on the relevant electrochemical impedance spectroscopies (EIS) expressed in terms of dispersions of the impedance with frequency (1 KHz-1 MHz). The measurements are performed in the different electrolyte solutions (NaCl, MgCl2, LaCl3, KCl, K2SO4, and K3PO4) with different concentrations ranging from 1 x 10(-4) mol/L to 6 x 10(-3) mol/L After that, the corresponding equivalent circuit as a theoretical model is set up. Experimental results indicate that the resistance of active layer is influenced by the concentration and ion species of electrolytes, while the capacitance is independent of them. For different cations and anions the corresponding resistances of the active layer take on a sequence of SO42>Cl->PO43- and Na+>La3+>Mg2+ respectively, which is in well agreement with the variation trend of ion retention, especially for monovalent and divalent ions. Furthermore, the thickness of the active layer in the working state is estimated from the capacitance values and compared with the result obtained by SEM. On the basis of the above, it is reasonable to think that EIS can be used for online analysis in membrane process. (C) 2010 Elsevier B.V. All rights reserved.