Formation of the complexes of alkaline earth metal ions with malonate and o-phthalate ions in aqueous, ethanol-water and acetone-water solutions (20% by volume) was studied at room temperature by the equilibrium ion exchange technique. This technique involved the measurements of distribution of radioactivity between cation exchange resin(Ion Exchange Resin CGC 241) and solution phases after the radioactive metal ions were equilibriated with the cation exchange resin in the presence of malonate or o-phthalate ions of varying concentrations. The pH of the solutions was controlled to 7.2~7.5, and the ionic strength of the solutions was kept at 0.10~0.11. The results of the present study indicated that the alkaline earth metal ions formed one-to-one complexes with the dibasic organic acids in all solvent systems examined. The present study showed that the relative stabilities of the complexes increased in the order: $Ba^{++};<;Sr^{++};<;Ca^{++}$ complexes. It was also observed that the relative tendency of the o-phthalate ion for the complex formation was somewhat greater than that of malonate ion in each solvent system. Furthermore, it was noted that the complexes were formed more readily in the mixed solvent than in the aqueous solution.