Carbonatite dykes and alkaline basic dykes are widely distributed in Bayan Obo. A study on their petrology, mineralogy, petrochemistry, REE and trace elements indicates that carbonatite dykes are igneous carbonatite, and REE content of some dykes is 14.675%, similar to that of dolomite carbonatite, implying that the two kinds of carbonatite are both REE-rich rocks. K2O+Na2O content of basic dykes in the ore district is higher than that of general basic rocks, suggesting that these dykes are alkaline rocks and belong to alkaline basic dykes. Carbonatite dykes are similar to alkaline basic dykes in REE and trace element patterns, and they also have similar Sr, Nd and Pb isotopic characteristics. These features indicate that the two kinds of dykes were formed in a special and similar source area, thus genetically related to each other.