Abstract: In this paper, the authors conducted for the first time Re-Os isotope analysis of molybdenite from the Bilugangan porphy-ry Mo deposit in Abag Banner, Inner Mongolia and obtained the molybdenite Re-Os isotope modal ages between 236.9± 3.7Ma and 238.7± 2.4Ma and weighted average value of 237.9± 1.7Ma, which indicate that the mineralization of Bilugangan Mo deposit oc-curred in Indosinian period. The average rhenium content of molybdenite is 74.065× 10^-6, suggesting the source of rhenium was char-acterized by mantle-crust mixing. Belonging to a porphyry Mo deposit, the deposit is located within the Slonker-Huolinguole arcbasin system of Da Hinggan Mountains-Inner Mongolia orogenic belt south of Hegenshan fault belt. Controlled by internal or exter-nal contact zones, the Mo orebodies are mainly situated inside the biotite granite porphyry and hornstone. The controlling or hosting faults in the contact zones are principally in NW, NE and approximately EW directions, and are filled with quartz veins. The stronger the development of stringer and stockwork quartz veins, the stronger the molybdenum mineralization. Regional researches reveal that Indosinian is one of the most important Mo(W) mineralization stages in Da Hinggan Mountains-Inner Mongolia orogenic belt and the adjacent areas in spite of the fact that this kind of deposit was discovered for the first time in this region. The results obtained by the authors provide important references for the further study of ore-forming regularity in the Slonker-Huolinguole metallogenic belt.