Apatites from carbonatite dykes and coarsegrained orehosted dolomite marble in Bayan Obo, Inner Mongolia, China, are systematically analyzed with the electron mic roprobe analyzer, indicating that they are similar in chemical compositions, bel ong to fluorapatite bearing strontium and rare earth elements (REE), and have ch aracteristics of carbonatitic origin. However, there are differences in REE patt erns and light REE fractionation between these apatites, revealing that they und erwent different influence by fluids bearing fluorine and REE that might be deri ved from evolved carbonatite rather than those related to granite or subduction. In other words, the apatite from coarsegrained dolomite marble is affected mo re heavily by the fluids than that from the carbonatite dykes.