Over the area between Beipiao City and Yixian County, Liaoning Province, there outcrop trachyte-tra-chyandesite volcanic rocks of the Upper Jurassic Zhangjiakou Formation and sedimentary bed of the Dabeigou Formation. The 40Ar-39Ar datings of the volcanic rocks of the Zhangjiakou Formation give an age of 143. 9 Ma. The most recently defined basalt member in the lower part of the Cretaceous Yixian Formation was dated at 137 -129 Ma, while the andesite member in the upper part at 126-120 Ma. It is ascertained that sedimentary rocks with Confuciusornis, i. e. the Jingangshan Formation around Sihetun, being considered as a part of the Yixian Formation, are of 123-120 Ma in age. Based on fossil records, isotope ages and the strata sequences of the Yanliao (Beijing-Hebei-Liaoning) area, it is considered that Confuciusornis and the beds containing such fossils should belong to the Early Cretaceous.