The Central Asian Orogenic Belt (CAOB) is the largest Phanerozoic accretionary orogenic belt on Earth, and central Inner Mongolia is widely regarded as the key segment marking the final closure of the Paleo-Asian Ocean within the CAOB. As a critical region for constraining the tectonic transition that followed the closure of the Paleo-Asian Ocean, central Inner Mongolia has long attracted considerable attention owing to its complex tectono-magmatic evolution. In this study, the monzogranite exposed in the Wulantaolegai area was investigated through petrography, whole-rock major- and trace-element geochemistry, LA-ICP-MS zircon U-Pb geochronology, and zircon Hf isotopic analyses to constrain its emplacement age, magma source, and tectonic setting. The results show that the monzogranite yields a zircon U-Pb age of 259.2±3.8 Ma (MSWD=1.2), indicating emplacement in the Late Permian. Whole-rock geochemical data indicate that the pluton is characterized by high silica (SiO₂=73.43%~75.15%), elevated Al₂O₃ (13.32%~14.24%), high total alkalis (Na₂O+K₂O=8.18%~8.61%), and low Fe-Mg contents, with aluminum saturation indices (A/CNK) of 1.05~1.11. It is enriched in light rare earth elements and large-ion lithophile elements such as Rb, Th, and K, but depleted in heavy rare earth elements and in Nb, Sr, P, and Ti, and is dominated by negative Eu anomalies, thus belonging to weakly peraluminous Ⅰ-type granite. Zircon Hf isotopic compositions yield εHf(t) values of -16.44 to -2.04 and two-stage Hf model ages (t_DM2) of 2 322~1 413 Ma, suggesting that the magma was derived predominantly from partial melting of ancient crustal materials, with the possible involvement of a very minor depleted component. In combination with the regional tectono-magmatic evolutionary framework, we propose that the Late Permian monzogranite in the Wulantaolegai area was generated by crustal remelting under a post-closure lithospheric thinning or extensional regime following the closure of the Paleo-Asian Ocean, indicating that central Inner Mongolia had entered a post-collisional to post-orogenic extensional tectonic regime by the Late Permian.