In mixed micellar systems of sodium bis(2-ethylhexyl) sulfosuccinate and long chain alkyl amines, such as tri-n-octylamine and bis(2-ethylhexyl) amine, the extraction of proteins and water are investigated, Extraction of water into the mixed micellar systems, which affects protein extraction, is controlled by pH in the aqueous phase. When the amine concentration is equal to or higher than that of AOT, no extraction of water is observed in the acidic pH range. The pH dependence on eater extraction is affected by the basicity of the amines added. Reverse micelles do not form from the mixture of AOT and cationic species of long chain alkyl amines in the acidic pH range. Extraction of proteins, such as low molecular weight lysozyme and higher molecular weight BSA, is also controlled by the formation of the reverse micelles, The formation of aggregates of proteins triggered by the electrostatic interaction with AOT is suppressed in the mixed micellar systems, The proteins extracted into the mixed micellar systems can be successfully back-extracted by destruction of the micelles at acidic pH.