Abstract: Airgin Sum monzogranite plution is located in western Xilin Gol-Airgin Sum Precambrian block, Inner Mongolia. Its age of 418.5± 1.1Ma obtained by LA-MC-ICP-MS U-Pb zircon dating means that Airgin Sum plution was formed at the end of Late Silurian. Its petrology and geochemistry show that Airgin Sum monzogranite is characterized by high silicon (SiO₂ 74.22%~75.51%) and rich potassium (K₂O 5.41%~5.78%)in association with A/CNK ratios ranging from 1.17 to 1.21, suggesting high-K and calc-al-kaline strongly peraluminous granite. The monzogranite is strongly enriched in Rb, Th, U, Pb, K and heavy rare earth elements (Yb 3.74× 10^-6~9.65× 10^-6) and is also characterized by depletion of Nb, Ta, Ti and P. It is suggested that the strongly peraluminous mon-zogranite was formed in the post-collisional setting and resulted from partial melting of crustal material after exhumation of overthickened crust. It is thus concluded that the northern orogen in Airgin Sum-Sonidzuoqi had collided between arc and block before Late Silurian, followed by an post-collision and post-orogenic extension setting during Upper Silurian-Middle Devonian.