The Pa'nan deposit is a newly-discovered porphyry Mo deposit at the eastern edge of the Chongmuda-Nuri ore field in Shannan Prefecture of Tibet. According to field work, the vein-like monzonitic granite-porphyry related to mineralization intruded into the Paleocene granodiorite, resulting in strong molybdenite mineralization and hydrothermal alteration in the porphyry and the contact zone. The molybdenite mineralization was mainly related to the straight quartz vein where most molybdenite occurred with a minor impregnation in quartz veins near the surrounding rock. In this paper, direct Re-Os isotopic dating of molybdenites collected from the quartz-molybdenite veins in the Pa'nan porphyry Mo deposit was carried out, which yielded model ages ranging from 31.34 to 31.83 Ma, a weighted average age of 31.66±0.22 Ma and an isochron age of 32.4±1.5 Ma (MSWD=1.5). The model ages and isochron age are consistent within the error range. Therefore the data represent the ore-forming age of the Pa'nan deposit, which is basically consistent with the previous studies which suggest that the mineralization of the Chongmuda-Nuri ore field occurred in Oligocene (30～23 Ma). These data indicate that the Pa'nan deposit had a similar deep dynamic progress to the other deposits in the Chongmuda-Nuri ore belt. Nevertheless, the metallogenic epoch of the Pa'nan porphyry deposit is slightly earlier than that of the other deposits in the Chongmuda-Nuri ore belt, suggesting that mineralization was probably started at ca.32 Ma and related to the delamination of post-collision thickened mantle lithosphere.