Zircon U-Pb ages have been determined for basement gneisses in the Bayan Obo REE-Fe-Nb deposit. On the U-Pb concordia diagram data of three samples yield up-per intercept ages of 1948-1917 Ma. Thus, these basement gneisses are of Paleoproterozoic. Rock association of these basement gneisses includes tonalite, syenite and paragneiss, not belonging to a sedimentary package. It is more appro-priate to consider this association as a basement complex rather than a stratigraphic “Group”. Zircon U-Pb ages have been determined for basement gneisses in the Bayan Obo REE-Fe-Nb deposit. On the U-Pb concordia diagram data of three samples yield up-per inter ages of 1948-1917 Ma. These basement gneisses are of Paleoproterozoic. Rock association of these basement gneisses includes tonalite, syenite and paragneiss, not belonging to a sedimentary package. It is more appro-priate to consider this association as a basement complex rather than a stratigraphic “Group ”.