Abstract: The Wulandele molybdenum-copper polymetallic deposit in Sonid Zuoqi, Inner Mongolia is a newly discovered large deposit during the geological survey in the Erlian-Dongwuqi metallogenic belt of Inner Mongolia. As a typical porphyry molybdenum deposit, its major ore bodies mainly occur in the fine-grained monzonitic granite with veinlet-disseminated ore, mediumfine grained granodiorite and fine-grained quartz diorite with disseminated ore. Molybdenite from the veinlet-disseminated ore hosted by granodiorite between 211.2 m and 214 m in the drilling hole of WZK1, is dated and its Re-Os isochron age is （134.1±3.3） Ma. Meanwhile the SHRIMP zircon U-Pb age of the fine-grained monzonitic granite is （131.4±1.6） Ma. These precise dating results represent the ore-forming period of this molybdenum deposit, the main dominant geological events and suggest its close relationship with buried Yanshan fine-grained monzonitic granite. It also indicates that the more attention on mineralization related to the tectonic-magmatic activities in the Late Yanshanian period should be paid in future prospecting.