Abstract: The water contents (Wo) of reverse micelles formed in a polar solvents by the addition of phosphatidylcholine(PC), phosphtidylethanolamine(PE)and the mixed system PC/AOT and PE/AOT have been studied. In a reverse micelle system Wo reflects the micelle size. The performance of extraction of proteins by these system has also been investigated. An assay was developed to determine the protein concentration in apolar phase in the presence of PC or PE. It was shown that the reverse micelles formed by PC or PE could not extract lysozyme, ribonuclease-a and cytochrome-c. The results of Wo measurement indicated that adding PC or PE to AOT reverse micell system made the reverse micelles much larger. Adding PE to AOT reverse micelle system increased the solubilities of some proteins in apolar phase, while adding PC to AOT system usually decreased the solubilities. It seems that the main factor affecting the extraction of proteins by reverse micelles is not the size of reverse micelle, but the interaction between the micelle and the proteins.