Abstract: Palynological research plays a significant role in exploration for petroliferous basins. It provides not only evidence for stratigraphic classification, but also information on paleovegetation and paleoclimate. With the palynological assemblages of the Well LS33 from the deepwater area of the Qiongdongnan Basin, this paper discussed the paleovegetation types and paleoclimatic characteristics of the basin since Oligocene. Eight palynological assemblages are identified and variations in assemblages recognized. The Early Oligocene pollen assemblages is dominated by ferns, accompanied by evergreens, with little cool and dry species, representing a tropical or subtropical warm and humid climate. The Late Oligocene to Early Miocene assemblages inherited the warm and humid weather in Early Oligocene. Quercoidites and Momipites are most abundant, with more apparent vertical zonations in both vegetation and climate. However, a stunning change occurred in Early Miocene. An increasing in pollen assemblage of temperate deciduous forest and alpine coniferous forest suggests the climate conditions that changed dramatically to cool and dry. Evergreens and Mangrove were abundant in Early Miocene to Late Miocene, and the climate was warm and humid then. Since Late Miocene, mangrove gradually reduced while herbs increased, which illustrated a conversion from the warm and humid weather to the cool and dry again.