Extraction behavior of active and denatured alpha -chymotrypsin is investigated by the reversed micellar extraction technique. The anionic surfactant dioleyl phosphoric acid (DOLPA) selectively extracted the active protein over the denatured protein. However, the reversed micelles using AOT do not afford selectivity. Based on the difference in the structural properties between the active and the heated alpha -chymotrypsin, the extraction behavior by the DOLPA reversed micelles is discussed.