Abstract: The Bayan Obo and Chaertai Groups are two important ore-bearing rock series,but their ages remain controversial for many years,and there is still an appreciable divergence of views as to the correlation between the two groups. In this paper an attempt is made to apply isotope geochronology,which has proved an effective means for age determination of rocks and minerals, in providing a basis for solving the above-mentioned problems. The author and his colleagues have collected and processed the available isotopic age data of the middle Proterozoic Bayan Obo and Chaertai Groups in the Bayan Obo,Chaertai Mountain and Lang Mountain areas,and analysed and discussed the age data obtained by use of the Pb,U-Th-Pb,Rb-Sr and K-Ar methods.On that basis and in combintion with various data regarding regional geology,stromatolites,paleomagnetism,lithogeogrprhy and characteristics of mineral resources,preliminary opinions have been put forward about the ages of the Bayan Obo and Chaertai Groups and their stratigraphic correlation.