The eastern Tanggula Range in the hinterland of the Qinghai-Tibet plateau constitutes the key to the reconstruction of the eastern palaeo-Tethys tectonic framework. It paleogeographically belongs to the eastern margin of northern Qiangtang basin, lies in the western part of the Sanjiang tectonic belt and is adjacent to the Emeishan Large Igneous Province. Volcanic rocks are widely distributed in the eastern Tanggula Range, with the volcanic activity taking place mainly in Middle Permian. Based on field mapping, the authors divided the volcanic rocks in Moyan area into three basic rock units, namely 2nd, 3rd and 4th rock unit, with the 3rd unit occurring in the interlayer form. They are in conformable contact with fine clastic rocks, mudstone and bioclastic limestone of the shallow-sea facies, making up three cycles of sedimentary-volcanic rocks in the Middle Permian Gadikao Formation. A systematical analysis of major and trace element compositions and whole-rock isotopes of the Gadikao Formation volcanic rocks indicates that the volcanic rocks belong to basalt (i.e., Moyun basalts) in the petrologic and geochemical indicators, with the rock types comprising grayish green massive basalt，grayish green massive olivine basalt and thick dark grayish green dolerite. The Moyun basalts have low and insignificantly varying SiO2, Al2O3, MgO, Ni and Cr content, being 44.24%～49.62% (averagely 45.62%), 12.27%～15.35%, 5.88%～7.52%, 112×10-6～191×10-6 and 141×10-6～269×10-6, respectively; K2O content varies remarkably (0.02%～1.27%), Mg# ratios are low (0.39～0.48), and there are high Na2O (2.36%～5.26%), TiO2 (2.12%～5.73%), total FeO (TFeO＞10%) and P2O5(0.70%～1.87%), suggesting that the Moyun basalts are similar to Emeishan continental flood basalts with high TiO2 and low Al2O3 content.As for geochemical characteristics, the Moyun basalts are of the transitional basalt series. The chondrite-normalized REE patterns indicate that all the samples have extremely high total content of rare earth elements (∑REE=284.02×10-6～678.88×10-6) and are significantly enriched in light REE (LREE), with (La/Yb)N of 14.89～23.23, (Gd/Yb)N of 2.30～3.58, and weakly Eu negative anomalies whose δEu values are 0.76～0.99.The large ion lithophile elements (LILE) (Ba, Th, Pb) and high field strength elements (HFSE) (Nb, Ta, Zr, Hf, P, Ti) in the basalts have been strongly concentrated. In the primitive mantle-normalized pattern, all the samples show weak negative anomalies of Nb-Ta, Zr-Hf, obvious negative anomalies of K, Sr and prominent positive anomalies of Th, La and Sm Rb/Sr, Zr/Ba, Ta/Hf, Nb/Zr and Th/Ta ratios are mostly in the range of 0.001～0.012 (averagely 0.006), 0.71～4.65, 0.22～0.56(averagely 0.36), 0.2～0.3 and 3.35～16.93, respectively The age-corrected initial (87Sr/86Sr)i ratios are low and vary narrowly from 0.703 3 to 0.703 9,143Nd/144Nd ratios are high (0.512 711～0.512 713), and εNd (t) values are +4.2 (t=271 Ma ). These data indicate an insignificant crustal contamination. In the diagrams of (87Sr/86Sr)i－εNd(t) for basalts, the data are fallen in the depleted mantle (DMM) area. It is thus concluded that the Moyun basalts are geochemically similar to intraplate basalts, characterized by both DMM and enriched mantle (EMⅠ). The basaltic magma might have been derived from lower degree partial melting of a garnet-bearing peridotite lithospheric mantle. The characteristics of the Moyun basalts reveal that their formation was closely related to the mantle-plume activity. The basalts must have been formed in an intraplate spreading zone (incipient rift) and have characteristics of the active rift. The data presented in this paper are of great significance for the study of the mantle evolution of the eastern Tethys in the Permian period.