Abstract: Early Yanshanian (Jurassic) granites, which are dominated by weakly peraluminous biotite monzogranite and K-feldspar granite, are ubiquitous in Nanling Range in Southeast China. However, the petrogenesis of the granites remains controversial.The Dadongshan pluton consists of biotite monzogranite and biotite-bearing K-feldspar granite. SHRIMP U-Pb zircon dating of two samples yield ages of 165 ± 2 Ma and 159 ± 2 Ma, consistent with the major formation time of the“ Nanling-series” biotite granites in the neighboring region. The granites are silica-rich (SiO2 > 72%), potassic (K2O/Na2O > 1.6), weakly peraluminous (most have ASI=1.00 ~ 1.11) and enriched in alkalies (K2O+Na2O = 7.4% ~ 9.3%). Samples are invariably enriched in Rb, Th and LREE, yet depleted in Ba, Nd, Sr, P and Ti, with distinct negative europium anomaly (δEu=0.06 ~ 0.34). Low contents of Zr+Ce+Nb+Y (< 350 ppm) and low 10000 × Ga/Al rule out their A-type affinity. Isotopically, samples show high and variable initial Sr ratios (0.7123 ~ 0.7193), yet low and constantεNd(t) (-9.3 ~ -11.5), corresponding to T2DM age of 1.70 ~ 1.89 Ga.However, their zircon Hf isotopes show large variations, withεHf(t) values between -3.5 and -11.8. Mineralogical and geochemical features suggest that the Dadongshan granites are highly fractionated I-type granites. They were probably derived from partial melting of the Proterozoic igneous protoliths with minor addition of juvenile crust or newly mantle-derived magmas, accompanied by assimilation and fractional crystallization.