This paper studies the formation age and geochemical characteristics of the volcanic rocks of the Manketouebo Formation in the Horqin Right-Front Banner area, Inner Mongolia. The LA-ICP-MS zircon U-Pb dating of two typical rhyolite samples reveals that the eruption occurred in the Late Jurassic (145.9±1.0 Ma and 146.0±1.3 Ma, respectively). The volcanic rocks of the Manketouebo Formation in the study area belong to the peraluminous, high-potassium calcium-alkaline series, with high SiO₂ (63.28%~77.40%, with average of 71.06%) and total alkalis (7.52%~10.14%, with average of 8.66%). The trace element patterns are characterized by enrichment of large ion lithophile elements (e.g., Rb, K) and depletion of high field strength elements (e.g., Nb, Ta, Ti, P), showing the typical characteristics of crust-derived magma. The rhyolite and trachyte in Manketouebo Formation have a good evolution trend in the major and trace elements. It is speculated that the crust-derived material was partially melted and erupted after different degrees of fractional crystallization. Besides, the volcanic rocks have similar geochemical characteristics of post-orogenic magmatism. Combined with the temporal and spatial distribution that the ages of the Manketouebo Formation in the Da Hinggan Mountains increase from southwest to northeast, it is proposed that the volcanism of this period is closely related to the post-orogenic extension after closure of the Mongol-Okhotsk Ocean.