The Haobugao polymetallic district in Inner Mongolia is located within the Huanggangliang—Ganzhuermiao metallogenic belt of the southern Great Hinggan Mountains. Skarn Zn—polymetallic, porphyry Mo, and granite- hosted Sn mineralization occurred during the Mesozoic magmatic intrusion. However, the relationship of the granite- hosted Sn mineralization with skarn Zn—polymetallic and porphyry Mo mineralization remain obscure, and are poorly understood.Methods: In this paper, based on detailed field geological work, granite- hosted Sn ores in the Wulanba pluton are investigated as an ideal objective. Two cassiterite samples were collected to date the U- Pb ages via LA- MC- ICP- MS method.Results: They yielded U- Pb Tera- Wasserburg lower intercept ages of 148. 7±5. 1 Ma and 146. 4±3. 4 Ma, respectively. The data suggests that granite- hosted Sn mineralization at Haobugao is coeval with the emplacement of the alkaline granite in the middle part of the Wulanba pluton (148. 9~142. 0 Ma), and thus indicating a consistency in space and time.Conclusions: Combined with previous studies, we propose that granite- hosted Sn mineralization can be spatially, temporally and genetically related with skarn Zn—polymetallic and porphyry Mo mineralization at Haobugao, and formed by the Late Jurassic—Early Cretaceous magmatism and related mineralization. In addition, the timing of Sn mineralization at Haobugao (148. 7~139. 6 Ma) coincides with that of large- scale Sn—polymetallic metallogeny in the southern Great Hinggan Mountains (150~130 Ma). We thus propose that, in combination with regional tectonic evolution, the Haobugao Sn—polymetallic district formed in an extensional tectonic setting.