The enrichment of rare earth elements is related to granites in the Hatu region in the eastern part of East Kunlun. Zircon U- Pb dating by LA- ICP- MS reveals that the crystallization age of Hatu syenogranite is 251. 6±1. 3 Ma. The Hatu syenogranite is high in SiO2 (74. 78%~75. 78%), Na2O+K2O (7. 68%~8. 11%), relatively low in Al2O3 (12. 58%~13. 06%), with A/CNK ratios ranging from 0. 96 to 1. 03, and displays metaluminous to weak peraluminous middle- K calc- alkaline affinities. The rocks are enriched in the large lithophile elements such as Rb, Th, Ba, Cs and LREE, depleted in the high field strength elements like Nb, Ta, Ti and HREE, possess low Nb/Ta ratio, high Mg# value and display obvious negative Eu anomalies (δEu=0. 67~0. 91). Based on the geochronological and geochemical data, it is demonstrated that the Hatu syenogranite has the characteristic of crust source and is the product of magma fractional crystallization, triggered by the underplating of mafic magma into lower crust. As the Hatu syenogranite has the characteristics of arc magmatic rocks, and in combination with the properties of magmatic and sedimentary rocks in the East Kunlun orogenic belt, it is inferred that the Early Triassic East Kunlun area is in the subduction stage of the Buqingshan- Anyêmaqên ocean. Large scale magmatic events resultedin the Early Triassic REE mineralization in the eastern part of East Kunlun.