PURPOSE: To remarkably improve the hydrogen ion selectivity by carrying out the immersion treatment of a specific hydrogen ion permselective membrane in a liquid containing nitrate ions.

CONSTITUTION: This method for treating a hydrogen ion permselective membrane comprises, carrying out the immersion treatment of (A) a hydrogen ion permselective membrane comprising a cation exchange membrane having an anion exchanger layer prepared by introducing a primary to a tertiary amino and/or a quaternary ammonium salt group into at least a part of an aromatic ring in an aromatic polymer having the aromatic ring in the main chain and a structure expressed by formula I [X and Y are each O or S; Ar is a group expressed by formula II to IV [W is a single bond, O, S, etc.; R1 to R5 are each a 1-8C hydrocarbon group; a is 0-3; [b+c] is 0-7; [d+e] is 0-5], preferably in at least a part of recurring units on at least one surface in (B) a liquid containing preferably 0.2-5.0mol/l nitrate ions.