An effective and practical radiochemical separation procedure of radiochemical neutron activation analysis (RNAA) for ultra trace rare earth elements (REEs) in silicate rock samples is presented. The procedure consists of two column separations of anion exchange and extraction chromatography and precipitations as hydroxide and fluoride of REEs. The most seriously interfering nuclide, Sc-46 is completely separated (<0.005%) from REEs by extraction chromatography using transuranic-element specific (TRU.Spec) resin. Chemical yields were determined by inductively coupled plasma atomic emission spectrometry (ICP-AES) and found to be constant within 3% for all REEs, implying that no fractionation occurs among REEs during the radiochemical purification procedure. By means of this procedure, other interfering nuclides than Sc-46 in RNAA of silicate samples were decreased down to <0.02% for Fe-59, <0.006% for Co-60 and <0.000005% for Cr-51. The RNAA procedure described in this paper can be one of the most suitable analytical procedures for accurately determining ultra-trace (1-10 pg) REEs in geological and cosmochemical samples. (C) 2003 Elsevier B.V. All rights reserved.