The oxygen and silicon isotopic compositions of minerals (quartz, feldspar and garnet) from the miarolitic cavity granites and pegmatites in Yunxiao county, Fujian province, are measured by using conventional method and laser probe analytic method for determining their material sources and forming conditions. The oxygen and silicon isotopic compositions of quartz and feldspar from the pegmatites are very similar to those of the granites, indicating that they have the same magma source. The Wushan granite in Yunxiao County mainly consists of Yanshanian aluminium Atype granite and its oxygen isotopic composition of the whole rock complies with the features of Atype granite. The temperature of 461℃ acquired for granite from the oxygen isotope fractionation between quartz and feldspar indicates that the granite might have experienced some extent water—rock interaction after crystallization, which is consistent with the extensive development of pegmatite miarolitic cavity in granite. Temperatures (ranging from 505℃ to 532℃) acquired from the oxygen isotopic fractionation formula of quartz—feldspar and quartz—garnet in the pegmatites suggest that the temperature of pegmatiteforming fluid should be about 500℃, higher than the temperature ranges by previous researchers. The silicon and oxygen isotopic ratios of garnet from the pegmatite were both significantly lower than those of coexisting quartz and feldspar in miarolitic cavity, indicating there are distinct fractionations of silicon and oxygen between garnet and quartz or feldspar, and both of which intend to share similar change pattern, but fractionation degree of silicon is smaller than that of oxygen.