Abstract: The Zhagawusu intrusive body is located close to the border between China and Mongolia and lies in northern Urad Middle Banner, Inner Mongolia. It mainly consists of diorite, quartz diorite, granodiorite and biotite monzonitic granite. The U-Pb age of zircons from the biotite monzonitic granite determined by LA-ICP-MS is 450.3±3.7Ma(MSWD=2.8).The rock samples are all characterized by strong enrichment of light rare-earth elements relative to heavy rare-earth elements, depletion of some high field strength elements such as Nb, Ta and Ti, high Sr, low Y and Yb content, and high Sr/Y and La/Yb ratios. The features indicate that the Zhagawusu intrusive body has a transitional normal arc/adakite geochemical affinity. The new age and geochemical data from the Zhagawusu intrusive body provide convincing evidence for Late Ordovician subduction of the Paleo-Asian Ocean in this region.