Abstract: In a process for electro-dialysis which comprises passing an electrolyte through dilution chambers and concentration chambers formed between a large number of alternately counterposed anion exchange membranes and cation exchange membranes, and applying an electric potential to a pair of electrodes provided at both ends of a plurality of these chambers, thereby migrating ions in the electrolyte through the membranes and effecting dilution or concentration of the electrolyte, such a volumic rate of air bubbles is introduced to the lower parts of the dilution chambers as to make the thickness of a diffusion layer formed by concentration polarization near the ion exchange membranes in the dilution chambers smaller than when air bubbles are not introduced thereto, and make the resistance between the electrodes smaller than when the air bubbles are not introduced thereto. Superficial air velocity of air bubbles introduced into the dilution chambers is preferably 1-4 cm/sec.