The partition coefficients of lysozyme and bovine serum albumin in poly(ethylene glycol) + dextran + water at 298.15 K are reported. The investigation focuses on the variation of protein coefficients with pH and total polymer concentration at constant temperature and constant polymer molecular weight. In addition, liquid-liquid equilibrium for the water polymer systems at different total polymer concentration as well as the difference in density between the top and bottom phases has been measured.