The Jehol biota is widely distributed in East Asia and characterized by the co-occurrence of Lycoptera, Eosestheria, Ephemeropsis trisetalis and Peipiaosteus pant associated with other fossils, such as feathered theropods, mammals, pterosaurs, fishes, reptiles, ostracods, bivalves, gastropods, insects and plants. This paper gives a brief historical review of the Mesozoic Jehol biota of China, sets forth the present situation in its definition, composition, stratigraphic distribution and geological age and discusses the Jurassic-Cretaceous boundary of terrestrial facies in China. Biostratigraphically; five assemblage zones can be recognized (in ascending order ): "Ephemeropsis trisetalis-Peipiaosteus pani-Nestoria pissovi " assemblage zone, "Lycoptera-Eosestheria-Cypridea" assemblage zone, "Sinosauropteryx-Confuciusornis-Jeholodens" assemblage zone, " Archaefructus-Protonemestrius-Changchengornis" assemblage zone and " Lycoptera muroii-Ephemeropsis trisetalis-Eosestheria" assemblage zone. According to biostratigraphic and isotopic data available, the Jehol biota may belong to the Early Cretaceous or range from the Latest Jurassic to the Early Cretaceous, because the GSSP of the Jurassic-Cretaceous boundary has remained uncertain yet. Anyway, it is impossible that the age of the Jehol biota is limited to the Late Jurassic.