More than ten mafic-ultramafic intrusions are distributed in Kuwei area of the Altay orogenic belt, and the Kuwei intrusion is the biggest one in this area. The SHRIMP U-Pb zircon dating yields an age of 47±1 Ma, suggesting thatstrong uplift occurred in this area during Cenozoic. Compared with the mafic-ultramafic instrusions in other areas of the Altay Mountains, the Kuwei intrusion has some unique geochemical features in that it is characterized by low TiO2, REE and incompatible element contents, and high Al2O3 contents. The wide range of MgO contents (6.6%～20.1%) and the correlation between MgO contents, othermajor element [CM(46]contents and Ni contents imply that the fractional crystallization of olivine, orthopyroxene and clinopyroxene might have occurred. Its low REE and incompatible element contents, flat chondrite_normalized REE patterns and incompatible element ratios (e.g., La/Sm and Gd/Yb) indicate that the primary magma resulted from the high degree of melting of the depleted asthenospheric mantle (garnet peridotite). In addition, its high La/Nb ratios and the markedly positive Pb anomalies in the primitive mantle normalized trace element patterns suggest that the magma must have been subjected to the contamination of low crust materials in the magma chamber. The relatively low Ni contents probably resulted from the immiscible sulfide melt at a relatively deep level.