Located in the Eren Nur area of China-Mongolia border region, the Qagan Dele amphibole_ and biotite-bearing monzogranitic pluton and the Weijing biotite monzogranitic pluton have zircon U-Pb ages of 276±2 Ma and 279±1 Ma, respectively. They are both Early Permian plutons. Geochemical data show that these two granite bodies have high SiO₂ (67.63%～74.75%), K₂O (2.94%～6.13%) values and weak Eu negative anomalies with A/CNK ratios less than 1.1, thus belonging to weakly peraluminous high potassium calc-alkaline series and exhibiting I-type granitoids features. Qagan Dele granites have zircon εHf(t) values between -18.65 to -10.95 and older model ages (t_DM2) in the range of 2470～1989 Ma, suggesting the probable existence of older crustral materials in the source. Weijing granites have zircon εHf(t) values between +1.71 and +5.44 and younger model ages (t_DM2) in the range of 1193～954 Ma, implying juvenile source at depth and crustal growth. Combined with regional tectonic evolution, it is held that these granitoids might have been formed in a syn-collisional to post-collisional setting. The fact that the two different plutons in the same area have different zircon Hf isotopes indicates completely different sources, which implies that recycling of old crust and crustal growth could occured in the same region.