Abstract: Various unique fossil insects, including 83 genera of 49 families, which are the most important members of the Jehol Entomofaunae, have been collected from Yixian Formation in western Liaoning Province, China. Biostratigraphically,the fossil insects are represented by the Ephemeropsis trisetalis-Sinaeschnidia cancellosa Assembalge, whose age is defined as the late Late Jurassic-early Early Cretaceous and obviously different from that of the Jiufotang Formation and Dabeigou Formation which are also assigned to the Jehol Entomofaunae in Northern Hebei and Western Liaoning. These sawflies can provide information about a warm and humid environment and indicate that different microclimates existed at the time,probably caused by topographic differences.