Abstract:The top of the Yixian Formation in the area western Liaoning, BeipiaoYixian, the Huanghuashan breccia or rhyolite above the Jingangshan bed of the Yixian Formation. Zircon of the rhyolite sample LAICPMS U-Pb dating gives weighted mean ages of 118.9 ± 1.4119.8 ± 1.9Ma. In addition, dacite porphyry injected into the lower part of the Huanghuashan breccia is dated by us Ing the 40Ar / 39Ar method, which has a plateau age of 122.1 ± 0.3Ma and an isochrone age of 121.8 ± 1.4Ma. These age data suggest that the top of the Yixian Formation in the area formed at BeipiaoYixian 122119 Ma. The determination of the age of the top of the Yixian Formation defines not only the upper age limit (~ 122 Ma) for the Rehe top part of the Yixian Formation Faunabearing (i. E. the Jingangshan bed) but also the upper age limit (- 118.9 ± 1.4Ma119.8 ± 1.9 Ma) of volcanic rocks of the Yixian Formation. The age of the top of the Yixian Formation in the area is also a very important ending age of Cretaceous magmatism in Western Liaoning Largescale and even Northeast China.