Water transference coefficients, water permeabilities and ionic transference numbers were investigated for the cation exchange membrane CR61 AZL389. The membranes were equilibrated with aqueous solutions of NaCl (KCI) and SrCl2 of various compositions. No chloride ions were detected in the membranes. The water transference coefficients and the water permeabilities were determined from streaming potential measurements, whereas the ionic transference numbers were determined by a new emf method. When the membrane was in the pure KM, NaM or SrM(2) form, the water transference coefficients were close to 11, 14 and 20, respectively. The water permeability is about two times larger in NaM than in SrM,. The water transference coefficient is not a linear function of the transference number of Na+ (K+) in the membrane, as found earlier. The results are explained by a variation in the membrane polymer cross-binding caused by Sr2+-binding to ionic membrane site(s). The transport behaviors in the mixture of NaM(KM) and SrM, can all be understood by the Sr2+ ion’s strong interaction with the polymer membrane.