[en] The known concentration of monazite is decomposed by various acids. The results show that sulfuric acid is the best acid decomposition, but the mixture of hydrofluoric acid and nitric acid or hydrochloric acid can decompose monazite ore only 5-6 percent. The selection of wavelengths for analysis must be appropriate for avoiding spectral interferences between individual rare earth elements. The individual rare earth concentration analysis by ICP-AES method and by NAA method are almost equivalent. The sum of individual rare earth oxide in monazite ores by ICP-AES method and the total rare earth oxide by ammonium oxalate gravimetric method are almost equivalent too