The processes of complex formation and extracting Gd, Er and Eu with 2-hidroksi-3-naphtoic acid (ONA) in the presence of pyridine (Py) have been studied. It is determined that the elements examined form with 2.3-ONA the anion complexes, composition and structure of which depend on ration of compounds and pH solutions. On the basis of carried out studies it is established that in the neutral and alkaline solution there takes place the formation of intra-complex compounds with chipping off hydrogens of carboxyl groups.