Abstract: The porphyaceous syenogranite pluton is exposed in the west of Qilian Country, Qinghai Province. The authors conduct-ed LA-ICP-MS zircon U-Pb dating of the porphyaceous syenogranite and the result shows that the age is 166.6±2.4Ma, suggesting the Middle Jurassic of Yanshanian period. Several inheritable magmatic zircons yielded the age information of the Precambrian peri-od. Geochemical data show that the porphyaceous syenogranite is silica-enriched in composition with high content of alkali, and hence it is a peraluminous granite and belongs to the high-K calc-alkaline series. It is characterized by enrichment of Rb, Th, K, de-pletion of Ba, Nb, P, Ti, and weak negative anomaly of Eu, with the average Rb/Sr ratio being 1.86, which reflects the characteris-tics of the crust source and indicates S type granite.