The Yamatu pluton in Nuoergong—Langshan area is located in the western part of the northern margin of the North China Craton. It consists mainly of monzogranite with many dioritic and gabbro enclaves. These enclaves have plastic shape and magmatic structure, quench boundary，backup veins and unbalanced textures, such as acicular apatite, quartz ocellar texture and plagioclase zoning. Geochemically, SiO2 of the enclave samples vary from 48.40% to 55.40%, and the contents of Fe, Mg, Ca and Ti in the enclave samples are higher than those of their host granites. The enclaves and their host granites have similar characteristic of major and trace elements, and show good linear relationship in Harker diagrams of the enclaves and their host granites.These characteristics suggest that there should be obvious genetic relationship between the enclaves and their host granites. The TFeO—MgO diagram of the enclaves and their host granite shows a very clear trend of magma mixing. Petrography and geochemistry also evidence magma mixing. The enclaves from the Yamatu pluton are probbaly derived from quenching of mafic magma into felsic magma.