During the Eocene-Oligocene transition (EOT) the global climate cooled from greenhouse" to "icehouse" at ca. 33.5Ma, which is one of the most prominent events during Cenozoic climate deterioration. However, few records of continental climate changes during this period are available,especially in Asia. To determine the behavior of Eocene-Oligocene continental climate changes, the Late Eocene to Early Oligocene sedimentary succession from the Xining Basin in the northeastern margin of the Tibetan Plateau was selected for pollen analysis. A total of 24 pollen samples were collected from the Mahalagou Formation of the Tashan section (36.5°N, 101.8°E), which is located ca. 7km south of Xining City. The section is 103.3m thick (ca.35.5Ma to 33.1Ma) and composed of red mudstones with 24 muddy gypsum or gypsiferous mud layers. Ten samples contained relatively rich pollen fossils. There were 109 palynomorphs belonging to 70 genus and 43 families. According to pollen variations from the lower to upper parts of the section,two spore pollen assemblages were established:I Nitrariadites-Meliaceoidites - Quercoidites (35.4 ~ 33.9Ma), II Quercoidites -Labitricolpites - Qinghaipollis (33.3 ~ 33.2Ma). In Assemblage I,high abundances of shrub taxa such as Ephedripites and Nitrariadites are found. In addition, thermophilic broadleaf taxa including Meliaceoidits and Rutaceoipollenites are also found. Others pollens such as the Quercoidites and Qinghaipollis are minor consituents. In Assemblage II, the proportion Ephedripites, Nitrariadites, Meliaceoidits is less than in Assemblage I. The abundance of herb taxa such as Labitricolpites and Qinghaipollis, however, is greater. Pollen analysis demonstrates that the vegetation of Xining Basin changed from Late Eocene semiarid warm sparse forest shrub to Early Oligocene arid temperate sparse forest grassland. These results indicate that the cooling occurred at ca. 33.9~33.3Ma and is coincident with aridification in Xining Basin, which may correspond to the EOT global cooling.