Abstract:East Kunlun contains large areas of intermediate- acid intrusive rocks, providing a natural laboratory for the study of magmatism, and the Late Triassic A- type granites can provide new constraints for the tectonic evolution in this area. In this paper, we present a detailed investigation of zircon U- Pb dating, whole rock geochemistry and Hf isotopes of the Langmaitan syenogranite in the eastern segment of East Kunlun,in order to identify the chronology and petrogenesis of rocks, and provide a basis data for the evolution of regional tectonics. Syenogranite consists mainly of orthoclase, perthite, plagioclase, quartz, and a small amount of biotite. The zircon U- Pb dating yields an age of 231. 5±1. 7 Ma, indicating its emplacement in Late Triassic. The syenograniteis geochemically characterized by high SiO 2 (72. 36%~74. 58%) and rich Al 2O 3 (12. 76%~12. 89%); is relatively rich in K 2O (7. 52%~7. 89%), but poor in Na 2O (4. 0%~4. 25%), low in MgO and TiO 2; enriched in large ion lithophilic elements Rb, K, etc. , depleted in high field strength elements such as Ba, Nb, Ta, P, Ti, and displays significantly negative europium anomalies ( δ Eu=0. 04~0. 08). All these characteristics indicate that they are A- type granites. Mg# is between 0. 40 and 0. 43, the ε Hf( t ) value is between +2. 05 and +7. 53, and T DM2 ages between 782 Ma and 1132 Ma, indicating that the syenogranite involvement of mantle components in petrogenesis. Based on the comprehensive regional geology and the characteristics, it is concluded that the Langmaitan A- type granite formed by partial melting of juvenile crust and mixed with mantle- derived materials in post- collision extensional environment.