The separation of actinoids such as Am from lighter lanthanoids has been investigated based on the liquid-liquid extraction principle. An extractant, 5, 8-diethyl-7-hydroxy-dodecan-6-one oxime (LIX 63), is suitable for separation of actinoids heavier than Am from lanthanoids lighter than Eu. On the basis of extraction behavior, multistage separation has been performed by centrifugal partition chromatography (CPC) provided with a series of micro cells. A kerosene solution of LIX 63 was retained in a column as a stationary phase without any solid support. The element substituted for heavier actinoids was chromatographically separated from lighter lanthanoids by CPC.