Abstract: The Hahaigang W-Mo polymetallic deposit in Maizhokunggar County, Tibet, is a tungsten and molybdenum polymetallic deposit, which is the first one to be explored in the Nyainqentanglha metallogenic belt. The basic geological characteristics of this deposit have been briefly presented in this paper. The mineralization age of this deposit has been obtained by using Re-Os isotopic dating methods. The Re-Os model ages of the two molybdenite samples from the Hahaigang skarn-type W-Mo orebody are (140.1±2.8) Ma and (143.3±5.2) Ma, with an average age of (141.7±4) Ma. Dating results showed that the ore-forming age of this deposit is Early Cretaceous, and was probably the product of mineralization during the southward subduction and collision stage of the Bangong—Nujiang oceanic crust. The model age is earlier than the diagenetic age (about 126 Ma) of quartz porphyries from the Yaguila deposit and Dongzhongla deposit on its eastern side. The definition of this deposit's mineralization age has enriched the metallogenic series of the Gangdise—Nyainqentanglha metallogenic belt, indicating the fact of Early Cretaceous mineralization and at least four stages of molybdenum mineralization existing in the Gangdise metallogenic belt. Meanwhile, it has great significance on the study of regional magmatic evolution and mineralization, as well as on the regional prospecting prognosis.