A process for producing an alkali metal hydrogencarbonate by reacting an aqueous solution containing alkali metal ions with carbon dioxide in a prescribed crystallizer to precipitate crystals of an alkali metal hydrogencarbonate, and in this process a part of a slurry containing the alkali metal hydrogencarbonate crystals in the aqueous solution is withdrawn from the crystallizer and, after dissolution of a part of the crystals, it is returned to the crystallizer.