Abstract: The distribution of Ca, Co (Ⅱ) between aqueous sulphate solution and HDEHPin n-hexane, kerosene, cyclohexane, carbon tetrachloride, methyl isobutyl ketone, toluene, benzene and chloroform has been studied at 25±1℃ respectively. The composition of the extracted species and the extraction constants were calculated and tabulated for different diluents. The distribution ratios decrease in the following order of diluents. n-hexane>kerosene >cyclohexane > carbon tetrachloride > methyl isobutyl ketone >toluene> benzene>chloroform.The results were discussed with the Lewis acidity and the solubility parameter of the diluents respectively.