The Fu’anpu molybdenum deposit lies in the east of the Xing’an Mongolian orogenic belt. The molybdenum ore bodies occur in the Yanshanian biotite granodiorite as quartz veins, and are controlled by fault structures. Fluid mixing is responsible for the Mo deposition. Re - Os isotopic ages for eight molybdenite samples range from 166.9 Ma to 172.3 Ma, with a weighted mean age of (168.22 ±0.87) Ma and an isochronic age of (171 ±3) Ma, respectively. It is indicated that the Fu’anpu molybdenum deposit was formed in the early Yanshanian period, and the corresponding geodynamic mechanism responsible for the Mo mineralization is related to the subduction of the paleo - Pacific plate.