Abstract: Located in Huade Country of Inner Mongolia on the northern margin of North China Block, the Sansheng W-Mo depos-it is a postmagmatic mesothermal deposit. Molybdenite Re-Os isotope analysis of the deposit was conducted in this paper, which yielded the weighted average value of the molybdenite model age of 138±1Ma and isochron age of 138.6±1.4Ma. In consideration of the age data, the authors hold that the Sansheng W-Mo ore deposit was formed in late Yanshanian period, consistent with the age data of the formation of main ore deposits in this region. Rhenium content in molybdenite is 0.5548×10^-6, indicating the crustal ori-gin. The ore-forming event resulted from large-scale Yanshanian tectonic and igneous activities and took place in an intracontinental tectonic environment.