A novel ion-exchange method which decreases byproducts and increases purity was developed for purification of amino acids in fermentation broth. The conventional method involves problems such as production of large amounts of byproducts and low purity of the product, since considerable amounts of the eluting agent remain in the effluent and the eluate. The new method employs hydrogen carbonate ions generated by dissolving carbon dioxide gas tinder pressure as the eluting agent, and this can easily be recovered from the effluent and the eluate after the ion-exchange reaction by releasing the pressure. Experiments were conducted using a strongly basic anion exchange resin (SA10A, Mitsubishi Chemical Corp.) and the fermentation broths of L-phenylaianine and L-glutamic acid as representatives of neutral and acidic amino acid, respectively. In the adsorption process, the ion-exchange reaction successfully proceeded under 0.5 MPa pressure by using compressed air in order to prevent the foaming of the carbon dioxide gas. It was possible to remove most of the hydrogen carbonate ions from the effluent by releasing the pressure and then concentrating the effluent. At the same time, it was also possible to recover the ammonia in the fermentation broth. Carbon dioxide gas dissolved in water or aqueous ammonia under 0.6-0.7 MPa was used for the elution of the amino acid. Almost all of the carbon dioxide gas was recovered by releasing the pressure in the cases of both L-phcnylalanine and L-glultamic acid. Therefore, it can be said that in both cases, favorable performances of elution were achieved. The results of this experiment Suggest that it is possible to construct a closed system in the amino acid production process.