The Youdong granite body, located in the central part of the southern Zhuguang granitic composite, is an important uranium-deposit-bearing granite. Its lithology is of medium-grained and small porphyritic two-mica granite. SHRIMP U-Pb zircon dating yields an age of 232±4Ma (MSWD=3.2) for the granite, indicating its formation by granitic magmatic activity in the early Indosinian epoch. The granite is rich in silicon (SiO2 average of 72.65%) and Al (A/CNK average value of 1.12) with high ratio of K2O/Na2O (average 1.79). It is also enriched in large ion elements including light rare earth elements, but significantly depleted in Sr, Ba P, Ti, Nb and Ta, with high ratios of Rb/Sr (average 8.08) and Rb/Nb (average 20.96). The rare earth element distribution patterns show right-inclining type with an significant Eu depletion. The Youdong has high (87Sr/86Sr)i ratios (average 0.72330) and low εNd(t) values (average -11.9) with old Nd model ages (average 1954Ma). These features consistently indicate that the Youdong body is a typical crustal–rock-sourced granite formed in an extensional tectonic environment that began shortly after the end of collision between the South China block and Indosinian block. In such an tectonic environment, the Youdong granite was formed by partial melting of Paleoproterozoic- Mesoproterozoic argillaceous and arenaceous rocks in the intermediate-lower crust sources under influence of lithosphere thinning and asthenosphere ascending.