The interaction of Y(III) and Ba(II) ions in the solid poly(vinyl alcohol) (PVA)-copper(II) acetate system with propionic acid was studied. Two kinds of coordination structures were detected in the films cast from an aqueous solution containing PVA and copper(II) acetate. One was a mononuclear Cu(II) complex, with the other being a binuclear Cu(II) complex of the cupric-acetate type. A significant decrease in the amounts of both of these complexes was observed on the addition of Y(III) and Ba(II) ions because of the formation of a multimetal polynuclear complex. The solubility of copper(II) acetate in aqueous PVA solution was increased by adding yttrium and barium acetates and attained its maximum level at a molar ratio of [Y] : [Ba] : [Cu] = 1:2:3. A precursor Y1Ba2Cu3Ox filament containing a large quantity of Y(III), Ba(II) and Cu(II) ions was shown to be beneficial for the generation of the superconducting phase by heat treatment.