One series of volcanic rocks, represented by pillow basalts, was found to occur in the lower Permian strata nearby the Wild Zoo Park, about 25 km east of Urumqi, Xinjiang. Two layers of the pillow basalts crop out along the road, with the thickness of 7~8m to the top layer and 2~3m to the bottom layer. The basalts occur as kidney, round, pillow, banded, wormlike or massive with the convex top and concave bottom. Long axis of basalt pillows are parallel and distributed along the strata surfaces. Some pillows trap a large amount of fossils, such as sea lily stems, coral and brachiopod. TAS diagram shows that most of the basalts belong to trachybasalt, while FAM diagram suggests that they belong to calcium alkaline basalt. K2OSiO2 diagram indicates that basalts are the lowK tholeiite to calcium alkaline basalt characteristics. The distribution of major elements is similar to that of island arc basalt. The trace elements distribution diagram indicates their origin of comagma and is of a highly similar evolution history. The trace elements determination diagram also shows an islandarc to backarc basin environment. Low total REEs amount, similar REE distribution, slight LREE enrichment and weak Eu positive anomaly reveal that the basaltic magma in eastern Urumqi experienced differentiation to some extent. REE distribution pattern of the basalt is similar to that of backarc basin basalt. The 283±8Ma of UPb age, along with stratigraphic and paleontological data, suggests that the basalt formed in the early Early Permian. Below the pillow basaltlimestone is a series of basal conglomerates, which was determined to be the boundary of Carboniferous and Permian. The medium to thick Early Carboniferous limestone occurring under the boundary has apparent karstification and unconformable contact, indicating the epeirogeny in the Late carboniferous but no orogeny. Geological and geochemical features of pillow basalts in eastern Urmuqi and their formation environment and time all indicate that the east Urmuqi region was an islandarc and backarc basin. Our study further confirms that the backarc basin formed from closureorogeny of northern margin of North Tianshan Mountain during CarboniferousPermian collision and subsequent relaxation expansion, accompanied by largescale intrusion of sea water. Finally closure time of collisional orogeny occurred likely in Late Permian. Due to the contamination of biofossils and terrestrial clasts, along with the addition of crust during its intrusion, the pillow basalts in eastern Urumqi, after its eruption, have complex geochemical features and multiple explanations. The study of the pillow basalt in eastern Urumqi is of great importance not only for understanding the tectonic sedimentary evolution and orogen in Bogda Shan, and even middle Tianshan Mountain during Late Mesozoic, but also for understanding formation and distribution of oilgas resources in Junggar basin, TurpanHami basin and Santanghu basin.