Abstract: In recent years, the oil and gas exploration in Yingen-Ejin basin keeps achieving significant findings and breakthroughs. However, stratigraphic division of drill holes and corresponding age of oil and gas reservoir remain much controversial. Some researchers hold that the reservoir would be Cretaceous layers, some opponents raise the idea of Permian. For the purpose of constructing stratigraphic succession in such a basin, No.1 Meng'edi well was drilled and cored in western Yingen-Ejin basin. Within this well, Estheria fossils were found in 930.5~958.0m section composed of gray to greyish green silty mudstone and mudstone layers, and in 1085.0~1095.5m section composed of dark gray mudstone layers, respectively. Therefore, Estheria fossils in the former well section were identified as Cyclotunguzites cf. gazimuri Novojilov, whereas those in latter section were identified as Hemicycloleaia ejinaqiensis Niu(sp.nov.) and Polygrapta neimengguensis Niu(sp.nov.). All of these Estheria fossils were assigned to the period of Permian. In addition to the evidence of stratigraphic correlation between drilling wells, the age of oil and gas reservoir was judged as Permian layers. Besides, Estheria fossils contain great indicating meaning in paleobiogeography. Based on comparing the distribution of Permian Estheria as well as analyzing the Carboniferous-Permian succession of Yingen-Ejin basin, the closing time of Paleo-Asian Ocean has been further constrained to Pre-Carboniferous.