On the basis of the latest available abundant information from field geological work, some important ideas about the lithostratigraphic classification and correlation of the Late Jurassic Yixi-an Formation in Jinzhou City and Yixian County, western Liaoning, have been supplemented and revised. According to the multiple stratigraphic division of the International Stratigraphic Guide, a complete column of lithostratigraphic units of the Yixian Formation has been erected. Based on the evidence of primitive fossil birds, together with the data afforded by other fossil groups (insects, fishes, reptiles, conchostracans etc. ), the age of the Yixian Formation is assigned to late Late Jurassic (about Tithonian).