Abstract:Due to the lack of outcrop data in the Yingen-Ejin Basin, the biostratigraphy was poorly studied. In addition, the stratigraphic division of drill cores and the corresponding age of oil and gas reservoir are still under controversial, either as Mesozoic or Late Paleozoic. In purpose of providing palynological evidences for the stratigraphic correlation of Yingen-Ejin Basin, pollen analysis was carried out to the bottom part of MED-1 core samples from Wuzhuer depression, western Yingen-Ejin Basin. According to the variations of the sporopollen taxa and their percentages, two palynological assemblages were recognized, the Osmundacidites-Deltoidospora- nonstriate bisaccate assemblage and the Classopollis-Cyathidites-Quadraeculina assemblage. In the first assemblage, the proportions of gymnosperms and ferns are close to equal. The nonstriate bisaccate taxa are diverse and abundant, while the striate bisaccate pollen only appears sporadically. Fern spores are dominated by Osumundacidite, and with the frequently appearances of Lycopodiumsporites, Deltoidospora, Neoraistrickia etc. Most of these taxa are common in Jurassic. The geological age revealed by the first palynological assemblage should be middle to late Early Jurassic, and the palynomorphs indicate a warm and humid climate at that time. Among the second assemblage, Classopollis becomes predominant, and Quadraeculina and Cyathidites show an increase than the last assemblage. No typical taxa of Cretaceous appear in this assemblage. The geological age should be assigned to late Middle Jurassic, and the climate turns to hot and dry during this period. According to the characteristics of the sporopollen assemblages, the strata previously designated as Upper Permian on the basis of Estherians fossils was redefined to be the Middle-Lower Jurassic, which providing new paleontological evidences for the stratigraphic correlation in Yingen-Ejin Basin. Yet, the revised geochronology and stratigraphy of Jurassic are well correlated in North China, and consistent with the evolution from coal rocks in humid and warm settings to eolian deposits of extremely hot environments.