Desorption properties of preadsorbed metal ions, whose valences are monovalent, divalent and trivalent , from sodium polyacrylate gel are investigated over the range of pH of buffer solutions. It is considered that in the gel which forms metal complexes, carboxyl groups combine with the metal ions according to their charge number stoichiometrically. From this fact, the desorption mechanism of the preadsorbed metal ions from the gel into aqueous phase is theoretically analyzed on the basis of dissociation equilibrium for polyacrylic acids and mass balance of the fixed carboxyl group species. Consequently, the model equations which allow quantitative consideration of the desorption mechanism in these systems, can be derived as a function of the hydrogen ion concentration, measured easily in the outer aqueous solution. The desorption equilibrium of monovalent, divalent and trivalent metal ions from the gel can be explained fairly well by the models.