Abstract: Mafic microgranular enclaves (MME) are distributed widely in Mid-Late Jurassic granite in the middle segment of the Nanling Mountains. There are more enclaves in the early-formed rock units than late-formed rock units in the same stage in the plutons. There are more and bigger enclaves in granites related to W-Sn-Mo-Bi polymetallic deposits and less and smaller enclaves in granites unrelated to mineralization. An integrated study of the colors, shapes, textures and structures, composition and lithology of the enclaves indicate that they are magmatic in origin. The occurrence of the disequilibrium mineral assemblage and textures and development of acicular apatite crystals and poikilitic quartz and alkali feldspar in the enclaves show the petrographic characteristics of magma-mixing, suggesting that the Mid-Late Jurassic granite formed by crust-mantle magma-mixing. In addition, study also indicates that Sn-mineralization is directly related to the degree of magma hybridization and the amount of introduced basic material.