The complex permittivity and electrical conductivity of saturated solutions of the Ba(HCOO)(2)-Cu(HCOO)(2)-H2O ternary system of water with salts was studied in the microwave range at frequencies of 13, 16, 19.25, and 25 GHz at 298 K, The static permittivity epsilon (s) and the dielectric relaxation time tau of the solutions were determined. The concentration curves of the dielectric parameters of the saturated solutions reflect the features of the trend of solubility isotherms and singular points of the ternary welter-salt system. Over the concentration range of crystallization of Ba2Cu(HCOO)(6) . 4H(2)O, the permittivity conserves a practically constant value, which renders this concentration range distinguishable with regard to intermolecular interactions. From additivity analysis of the contributions made by the binary systems to epsilon (s) variation in the saturated ternary solutions, complexing was shown to exist in concentrated ternary salt solutions. Both hydration and ion-ion association affect the permittivity and govern the trend of the solubility isotherm for the system in question.