In the present work, the batch distribution ratios of 9 lanthanide ions, Ce^3^+, Nd^3^+, Sm^3^+, Gd^3^+, Tb^3^+, Dy^3^+, Er^3^+, Yb^3^+ and Lu^3^+, ae measured by countercurrent chromatography (CCC) with 25% DHDECMP (dihexyl-N,N-diethylcarbamoylmethylene phosphonate) in cyclohexane as the stationary phase and 3.35 mol/L HNO~3 as the mobile phase. Although perfect separation of the lanthanide ions using this system is impossible, heavy and light lanthanides can be grouped. The light lanthanides are better separated from each other. The interested metals can be nearly completely recovered. The dynamic distribution coefficients (D^d^y^n) obtained from the chromatogram are not equal to but proportional to the batch distribution coefficients (D^b^a^t), althongh the D^d^y^n is often equal to D^b^a^t in the separation of organic solute. This discrepancy is attributed to that the mechanism of the separation of metal ions by CCC is different from that of the organic solute. The results are consistent with the theoretical predictions, indicating that CCC deserves to be explored as a method for investigating the mechanism of the extraction reactions.

Key words: COUNTER-CURRENT CHROMATOGRAPHY, RETENTION VOLUME, LANTHANIDE SERIES METALS, PHOSPHONIC ACID ESTER, CYCLOHEXANE