Dong Ujimqin Banner in Inner Mongolia is one of the most developed Devonian strata areas along the orogenic belt in northern China. Previous researchers determined the relative age of strata by fossils; however, there is no accurate isotopic age. In this paper, using LA-ICP-MS dating method, the authors determined zircon U-Pb ages of tuff interlayers in the upper part of Devonian Tarbaget Formation and acquired ²⁰⁶Pb/²³⁸U weighted average age of 380.8±1.6 Ma(MSWD=2.7), indicating an early Late Devonian age. This provides accurate geochronological data for Devonian strata in this area. Combined with the data of the fossil assemblage, the authors determined the age of Tarbaget Formation, which is middle Devonian Givetian period-late Devonian Frasnian period.