Abstract: The effect of the length and diameter of the absorbing column and the sepa-rating column packed with cation exchanger, the flow rate of the eluate, the load-ing of the samples (Eu, Sm, and Nd) and the pH values of the eluate of α-HIBAon the separation of Eu, Sm, Pm and Nd in the spent fuel are studied usingHPLC. A procedure for the separation using the best separation conditions is re-commended, The blank of Nd is (2.5±0.5)×10~(-8)g in the whole procedure whichstarts from dissolving fuel sample and ends in preparing Nd sample for mass sp-ectrometric measurement. The procedure is practical and gives good analytical re-sults as being verified by the mass spectrometric measurements of Nd and Sm andthe γ-spectrometry of ~(147)Pm and Eu.