The rare earth elements (REE) form the largest chemically coherent group in the periodic table. The versatility and specificity of the REE have given them a level of technological, environmental, and economic importance considerably greater than might be expected. The objective of this work was to determine the concentration of rare earth elements in phosphate samples from Egypt and Saudi Arabia, using both instrumental neutron activation analysis (INAA). The samples were prepared together with standard reference material and simultaneously irradiated in a neutron flux of 7 x 1012 n.cm-2 s -1 at ACTLAB activation laboratories Canada. Irradiated samples were measured using gamma-ray spectrometer based on HPGe detector. The choice of the nuclear reaction, irradiation and decay times and of the proper gamma ray measurement to determine the concentrations are presented and discussed