Transport of lysozyme through a liquid membrane of reversed micelles of aerosol-OT (AOT) was studied. The feed phase was aqueous KCI or NaCl solution of lysozyme, and the recovery phase was aqueous KCI or BaCl2 solution, while the membrane is the solutions of AOT with or without contacting the feed solution. The cations in feed phase are transferred through the liquid membrane and this cation transfer affects that of lysozyme and the size of reversed micelles of the membrane phase. Following transfer mechanisms have been proposed for the three systems investigated: the system NaCl-KCl, for which formation of large aggregates in the membrane phase was observed, has a so flexible interface that the micelles could become unstabilized in the membrane phase. For KCl-BaCl2 system, the divalent ion Ba2+ is selectively and excessively adsorbed on the interface and the negatively charged lysozyme molecules may be re-extracted at the interface of the recovery side by the electrostatic interaction with the adsorbed Ba2+ ions. Both sides of the interfaces of the system KCI-KCI have an adequate flexibility that extraction and back-extraction of lysozyme through the membrane are attainable, although the transfer rate is rather low.