The pK 1 and pK 2 values of maleic and malonic acids were determined by using a precise EMF method in acetone-water media of varying solvent compositions at different temperatures. The thermodynamic functions of dissociation (∆H • , ∆G • , and ∆S • ) have been computed, discussed and analyzed in terms of solute-solvent interactions. The pK values have been correlated with both the mole fraction of the organic solvent and the distance between the dicarboxyl groups in each acid.