Located in the East Qinling molybdenum metallogenic belt on the south margin of the North China craton, the Nannihu Mo (-W) orefield comprising Nannihu, Sandaozhuang, and Shangfanggou deposits is a superlarge skam-porphyry Mo (-W) orefield in the world. Re-Os dating was performed of six molybdenite samples from the Mo deposits in the Nannihu Mo orefield with inductively coupled plasma mass spectrometry (ICP-MS). The results show that the Re-Os model ages are 145.8±2.1-141.8±2.1 Ma for the Nannihu deposit, 145.4±2.0-144.5±2.2 Ma (averaging 145.0±2.2 Ma) for the Sandaozhuang deposit and 145.8±2.1-143.8±2.1 Ma (averaging 144.8±2.1 Ma) for the Shangfanggou deposit; dating of the six samples yields an isochron age of 141.5±7.8 Ma (2σ), which accurately determines the timing of mineralization. The results also suggest that the ore-forming materials were mainly derived from the lower crust, mixed with minor mantle components. These Mo deposits were formed during the transition of the Mesozoic tectonic regime in east China, and its mineralization was a part of the Late Mesozoic large-scale mineralization in that region.