Donnan dialysis with ion-exchange membranes was studied under various kinds of experimental conditions using ions of different valences. The diffusion coefficients (D-d) Of various kinds of ions in the ion-exchange membrane were obtained by curve fitting an equation derived from the mass balance to three kinds of Donnan dialytic experiments. It was found that the Value of D-d/D-s, using D-d Of monovalent ions in Donnan dialysis with a set of monovalent feed ions and bivalent driving ions was 1/175, where D-s, represents a diffusion coefficient in solution. D-s, was calculated from the Nernst-Einstein equation substituted by the ionic conductance of ions at infinite dilution in water. Using D-d Of bivalent ions in Donnan dialysis with the same set led to a D-d/D-s, value of 1/438. Moreover, using D-d in Donnan dialysis with the same set, the value of D-d/D-e, was kept constant at 0.4 (D-e, expresses the diffusion coefficient in the membrane when the valences of the feed and driving ions are equal). On the other hand, both D-d/D-s, and D-d/D-e, using D-d in Donnan dialysis with a set of bivalent feed ions and monovalent driving ions were not constant.