The Jehol Biota was a very prosperous biota preserved in lacustrine formations during the late Mesozoic of Eastern Asia, especially in western Liaoning and northern Hebei Provinces, China. Three typical representatives of it are conchostracan Eosestheria, nymphal mayfly Ephemeropsis and fish Lycoptera. Recently we collected and studied about one hundred fossil mayfly specimens from Yixian Formation of the Jehol Biota. By comparing our specimens with the imago specimens of Ephemeropsis Eichwald reported from Transbaikalia region of Siberia and Mongolia, we have established the genus Epicharmeropsis and its two species E. hexavenulosus, E. quadrivenulosus. We believe previouslydescribed specimens from the Yixian Formation, the socalled Ephemeropsis trisetalis, should be transferred into this genus too. Although Ephemeropsis Eichwald was widely distributed in Transbaikalia region and Mongolia, its reported finding in China is not supported by our study. In addition, the definition, stratigraphic correlation, geographical distribution of the Jehol Biota and river system during the Late Mesozoic are also discussed.