Polyethers, such as poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) were used as polymer solvents. PEO interacted with smaller cations more strongly, and formed stable complexes with the salts having lower lattice energy. In a mixed salt system, solvation state of cations should reflect the degree of ion-dipole interaction with PEO. As a result, the salt, which has higher lattice energy and larger cation, was phase separated by the addition of the other salt which was solvated stronger by PEO. A competitive solvation of salts was applied to phase separate the target salt from the PEO oligomer solution. Furthermore, the exchange of cations or anions of the phase separated salts was also observed during salt mixing. PEO was concluded to have an ability to solubilize certain salts preferentially and selectively reflecting the characteristics of the salts.