Abstract: In order to learn the characteristics of magma activity along the southern plate of Siberianlate during Late Palaeozoic Eta.,petrography,U-Pb chronology of the zircon,zircon Hf-isotopeand geochemistry of the Bayandulan monzonitic granite are studied to constrain the genesis and tectonic setting of the rock in Dong Ujimqin Qi,Inner Mongolia.Zircon U-Pb dating obtained by LA-ICP-MS analyses from the monzonitic granite is(277.2±0.7) Ma,suggesting that it is the production of magmatic activities in later period of Early Permian.The ε_Hf(t) values and the crust model ages(t_DMc) of Bayandulan monzonitic granite,are 6.8-14.1and 865-655 Ma respectively.The Bayandulan monzonitic granite is enriched in K(K=3.63%-4.95%,K₂O/Na₂O=0.91-1.47)and alkali(K₂O+Na₂O=7.52%-9.16%),suggesting the feature of metaluminous to weak peraluminous(A/CNK =0.96-1.15).It is apparently different in LREE and HREE,with most rocks having weakly negative Eu anomalies(δEu=0.34-1.17).The rock is depleted in rare earth elements(∑REE=38.82×10^-6-193.32×10^-6),and Sr,Nb,Ta,P,Ti enriched in partial LILE(LREE,Rb,K and so on)with weakly negative Zr anomaly and weakly positive Hf anomaly,showing characteristics of post-orogenic granites.The monzonitic granite produced in extent environment,and was the product of post-orogenic evolution after closing of the Hegenshan Ocean.And the formation of the rock is partial melting of juvenile continental crust resulted from subducted oceanic crust exised during 865-655 Ma.