Abstract: Huheengeer mafic-ultramafic complex is found in Bayan Obo region, Inner Mongolia. Petrographically, the complex shows a concentric zoning in rock distribution: hornblende-peridotite, hornblende-gabbro and diorite from core to margin successively. Characteristics of structure and chemistry of the pluton suggest that the rocks were derived from a gabbroicdioritic magma by crystal differentiation. The hornblende-peridotite and hornblende-gabbro were formed by cumulation of early crystallized mafic minerals, and the other rocks crystallized from a magma formed after cumulative process by eutectic crystallization. The parental magmas were compositionaeey similar to high-Al basalt and (or) basaltic andesite. The K-Ar apparent ages of the rocks are between 242-287 Ma. The major rock-forming minerals in the Huheengeer Complex are olivine, pyroxene,plagioclase and hornblende. Based on electron microprobe analysis (EMPA), pyroxene is diopside, and plagioclase is bytownite (An90.6) in amphibole gabbros. The complex also shows geochemical characteristics of enrichment in LREE, LILE (K，Rb，Sr，Ba), and depletion in HREE, HFSE (Nb，Ta，Zr，Hf). According to the AlZ-TiO2, An-Mg,, Hf/3-Th-Ta and Hf/3-Th-Nb/16 diagrams, the Huheengeer complex is suggested to be generated at an active continental margin. All the combined information indicates that these plutons are mafic-ultramafic complex of peritotite-diorite type and they should be a record of Paleoasian Ocean plate subduction to the northern side of North China plate in the Permian.