The adsorption of sodium oleate and potassium octyl-hydroxamate onto the rare-earths minerals monazite and bastnaesite was investigated through microflotation experiments, zeta potential determinations and infrared spectroscopy. The monazite and bastnaesite samples were purified in the laboratory reaching, respectively, final grades of 68.7 and 45.3% RE(2)O(3) + ThO2. The results confirm that sodium oleate chemisorbs onto bastnaesite and suggest a physical adsorption mechanism of this reagent onto monazite. Despite the lack of a full confirmation from FTIR spectrometry, there is a possibility of oleate chemisorption onto monazite in the pH range above the isoelectric point. A chemical adsorption mechanism was established for the interaction between octyl-hydroxamate and both minerals.