A new method is proposed here for determining counter-ions permselectivity through an ion exchange membrane. The theoretical base of the method is Henderson equation. After simplifying at special experimental conditions, a linear relationship between the bi-ionic membrane potential term and concentration ratio, i.e., [exp(z(A)F(-DeltaE(T))/RT) - 1] proportional to [C-A.L/C-B.L] can be obtained, from the slope of which, the permselectivity of counter-ions can be achieved. This method is very simple in operation and less time and money consuming. The method is exemplified by common 1-1, 2-2 and 2-1 counter-ions pair through a novel and published anion exchange membrane. The accuracy and the validity of the method is tested by three aspects: (1) the experimental [exp(z(A)F(-DeltaE(T))/RT) - 1] proportional to [C-A.L/C-B.L] curve approaches a straight line (2) the predicted order of counter-ions conforms to the results evaluated in a practical electrodialysis process; and (3) the results calculate from different referenced counter-ions for the same counter-ions pair agree well with each other. (C) 2004 Elsevier B.V. All rights reserved.