Abstract: The capabilities of α-hydroxy-α-methylbutyric acid (HMBA) and α-hy-droxyisobutyric acid(HIBA) for the cation exchange chromatographic separation of Am(Ⅲ)-Cm(Ⅲ) under the same conditions have been studied.The separation factor of these two elements obtained by using HIBA as eluant is 1.37 which is in accordance with the data given in the literature,while that obtained by using HMBA as eluant is 1.71. It can easily be seen from these data that HMBA is a better eluting agent for the cation exchange chromatographic separation of Am(Ⅲ)-Cm(Ⅲ) than HIBA.Many factors which could affect the effectiveness of Am(Ⅲ)-Cm(Ⅲ) separation using HMBA as eluent have also been studied in order to use HMBA as a practical eluting agent and it is found that quite satisfactory results of the cation exchange chromatographic separation of Am(Ⅲ)-Cm(Ⅲ) can be obtained using an eluting solution containing 0.3 to 0.4 mol/1 of HMBA in the pH range from 4.0 to 4.4 and in the temperature range from 25 to 70℃.