Xilinhot Block is located in the middle segment of the Xing- Meng Orogen in Inner Mongolia. Precambrian rocks in the block consists of Baoyintu Group and gneissic granite. Discovery of ~1.4 Ga Mesoproterozoic granitic rocks provides evidence for existence of the Xilinhot Block, but its petrogenesis and tectonic implication are still unclear. Mesoproterozoic granitic rocks in the Sonid Left Banner area consist mainly of yenogranite and monzogranite. And zircon LA- ICP- MS U- Pb dating for four samples yields ages of 1373±7 Ma and 1399±11 Ma, respectively, suggesting middle Mesoproterozoic in age. The gneissic granitoids are characterized by high SiO2 and alkali, with K2O/Na2O>1 and peraluminous, high total REE content with enrichment of LREE rather than HREE, and distinct negative Eu anomaly. All these features indicate that they belong to A2- type granite. The in- situ zircon Hf isotopic analysis shows depleted compositions with (176Hf/177Hf)i ratios varying from 0.281924 to 0.282288, εHf(t) values from +0.8 to +11 and two stage Hf model ages (TDM2) from 1.45 to 2.17 Ga. Generally depleted isotopic composition and whole rock εNd(t) of (+0.3~+1.0) except one sample with a value of -0.2 suggest that the gneissic granitoids were the product of partial melting of accretion crust in the end of the Paleoproterzoic (1.88~1.97 Ga). Regionally extensive occurrence of 1.4 Ga potassic granitoids displays occurrence of a tectonic- magmatic event triggered by crustal extension, which was response to breakup of Colombia supercontinent. 1.4 Ga A- type granitoids in the Xilinhot block indicate that the Xilinhot Block and North China Craton in the Mesoproterozoic both were in a tectonic setting of continental extension.