Abstract: In recent years, numerous fossil vertebrates, invertebrates and plants have been found in the Middle Jurassic Tiaojishan and Jiulongshan Formations in western Liaoning, southeastern Inner Mongolia and northern Hebei. This biota is called Yanliao biota. Up till now, 28 species of different vertebrate groups have been formally named, which include 1 fish, 4 amphibians, 1 lizard, 12 pterosaurs, 5 theropods, and 5 mammals. The vertebrates of this biota have great significance for studying the theropod evolution, the pterosaur classification, and the lissamphibian diversity. Although the diversity of the Middle Jurassic Yanliao biota is less than that of the Early Cretaceous Jehol biota, it provides important evidence for understanding the succession of the Late Mesozoic biotas in this region.