AbstractThe dependence of the upper and lower critical solution temperatures Tc of the systems (1) oxolane + water, and (2) 2‐butoxyethanol + water on the mole fraction XEl of dissolved 1‐1, 2‐1, and 3‐1 electrolytes has been investigated. The material stability of the homogeneous state of both systems is extremely sensitive to small electrolyte concentrations so that the observed shift of Tc may be interpreted as the result of a perturbation of the mutual solvation of both non‐electrolytes by ion solvation. Cations destabilize homogeneity in the order Me+ < Me2+ Me3+. The nature of the anions, however, for which the order Cl− > Br− > I− > NO−3 > ClO4− is established, determines whether the closed miscibility gap expands, shrinks, or is shifted to higher temperatures with increasing xEL. The importance of the anions is evident from a comparison of MgCl2 and Mg(ClO4)2, for which the lower critical solution temperatures of oxolane + water at XEl = 0.003 differ by about 70 K.