Abstract: The study of the Late Mesozoic deposits (generally called "Jehol Group" except for the uppermost Sunjiawan Formation) of western Liaoning was initiated early in this century, but the stratigraphic sequence of the Jehol Group, its correlation with the corresponding non-marine strata in northern China and the age assignment have long been controversial issues. The present paper is to deal with these problems mainly based on the data of fossil fishes. The Late Mesozoic lithostratigraphic succession in western Liaoning is adapted as follows (Table l): the Yixian (excluding the former Jingangshan Beds and Tuhulu Beds), Jiufotang, Shahai / Zhanglaogongtun, Fuxin and Sunjiawan formations in ascending order, and certain irregular or diachronous phenomena of lithostratigraphic nomerclature are recognized among the separate basins in this region, e.g., the current Yixian Formation in the western LingyuafrSanshijiazi and middle Chaoyang- KazuoJianchang basins can only becorrelated with the Yixian volcanic rocks and its base sedimentary horizon in the eastern Fuxin-Yixian-Jinzhou Basin, but the Jiufotang Formation in the western and middle basins is equivalent to the Jingangshan and Tuhulu beds plus the Jiufotang Formation in the eastern basin after the litho- and biostratigraphic principles. The igneous rocks over the Yixian Formation has long been ignored or misplaced, and its reasonable position in the sequence should be between the Jiufotang and Fuxin formations. The Jehol Group can be coincidentally correlated with the corresponding strata in other or basins of northern China on the basis of fossil fishes (Table 2). The loweß part (Yixian and Jiufotang formations) of the Jehol Group and its equivalents in northern China were generally originated in fluviolacustrine environment while the upper part (Shahai and Fuxin formations) deposited in deltaic and lacustroswamp facies. The Lycoptera and Kuyangichthys ichthyofaunas (Table 3) show a Late Jurassic and Early Cretaceous aspect, not a few forms are closely related with, •or quite similar to fishes found in the Upper Jurassic of Kazakhstan in central Asia, in the Purbeck-Wea1den of western Europe, and in the Lower Cretaceous of Kitakyushu in Japan. Based on the evidence of the fish faunae, together with the data afforded by other fossil groups, event stratigraphy and radiometric dating etc., the age of the Jehol Group and its corresponding strata in northern China is assigned to late Late Jurassic-mid Early Cretaceous (about Portlandian-Barremian).