A liquid-solid extraction system based on Tween 80/phosphate was developed. Under the optimized conditions (9 wt % Tween 80, 1.6:1 (molar ratio) K2HPO4:NaH2PO4, 1.25 mol/L total phosphate, pH = 7.4), alpha-Lactalbumin (alpha-La) and beta-Lactoglobulin (beta-Lg) were separated with recovery rates of 87.6 % (in the solid polymeric phase) and 98.2% (in the salt aqueous phase), respectively. Under the effects of water and salt, the solid phase had the ability to form a new liquid-solid extraction system, and 85.1% of alpha-La could be reversely extracted into the new salt aqueous phase. Following dialysis against water, proteins obtained through extraction and reverse extraction, were analyzed by polyacrylamide gel electrophoresis (PAGE) and thin-layer scanning. The method was applied successfully to separate alpha-La and beta-Lg from milk whey.