The solubility of salt in water decreases in the presence of a water soluble polymer, polyethylene glycol (PEG), and could be expressed by a linear relationship between the logarithm of the solubility of salt (M) and the concentration of PEG (M). The slope of the solubility lines was in agreement with the excluded volume of PEG calculated with the rod-like model of PEG. The solubility limit of each salt in the PEG-free solvent (solvent unoccupied by PEG) remained constant regardless of the concentration of PEG. Therefore, the solubility of salt in PEG solutions may be described by the excluded volume effects of PEG. This suggests that PEG sterically excludes salt, thus salt is concentrated in the accessible solvent up to the solubility limit.