Lysozyme extraction by mixed reverse micelles composed of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) and tetraethylene glycol phenylnonyl ether (PNE4) was studied. Taking into account the contributions of electrostatic and hydrophobic interactions

a theoretical model was established to describe the partitioning equilibrium. Experimental results demonstrated the reliability and usefulness of the model. It was found that the hydrophobicity of AOT was lower in the presence of Na+ than of K+

while that of PNE4 was independent of the cations. The enhancement of lysozyme surface hydrophobicity by Na+ was more significant than K+

while the adsorption ability of K+ on the inner surface of the reverse micelles was larger than Na+. Analyses and explanations of these phenomena were made by using electrostatic and thermodynamic theories.