There are a lot of microgranular enclaves in the late Yanshanian Qingtian biotite granite in southeast Zhejiang Province. The enclaves are generally round or sub-round with diameters from 10 to 20 cm. They are usually scattered but some of them occur in groups in the granite. The enclaves are often gray or dark-gray in colour. Generally, there are clear boundaries between the enclaves and host granite, but some show diffusion contact. A few of enclaves show fine-grained margins, i. e. chilled margins. The enclaves are mainly composed of plagioclase(An=37), hornblende, biotite, quartz, and K-feldspar. The plagioclase is zoned. Quartz and K-fel-dspar fill in the interval betWeen plagioclase, or enclose the microcrystal plagioclase and hornblendes to form intergranular texture which is similar to that of dolerite, or poikilitic texture. The accessory minerals include magnetite, ilmenite, apatite, sphene, etc. The apatite is very long with the ratio of length to width up to 30:1, and has clear basal cleavage. According to Wylie this kind of apatite is formed by sudden cooling of the magmaoc-existing with the apatite. Chemically, the enclaves belong to the calc-alkline rock serieswith SiO2=60-68%, Na2O>K2O, and A/NKC<1.In comparison to the host granite,the quartz-dioritic enclaves have higher contents of Ti, V, Cr, Co, Ni, Zr,Sr, Ca, Mg and REE. On the variation diagrams of major oxides versus SiO2 of the enclaves and the host granite, the plots show linear trends, and so do some pairs of trace-elements divided hy other trace-elements. There are different hypotheses about the origin of microgranular enclave in granitic rocks. The enclave may be regarded as xenolith, or the relict phase of partial melting of basement rocks, or a product of magma mixing,and so on. Based on field observations and petrological, geochemical, and mineralogical features of enclaves, the authors believe that magma mixing theory is most suitable for explaining the characteristics of the quartz-dio-ritic enclaves in the Qingtian biotite granite, namely, they were the products of mechanical mingling between basaltic or intermediate-basic magma and granitic magma.