Abstract: The Erlian Basin is located in central Nei Mongol(InnerBecause the definitions of some formations vary among localities or areas, the following dis-cussion of locality names, and the stratigraphic subdivisions and correlations is organized geo-graphically in order to avoid further confusion(refer to Fig.1 for the localities). Mongolia), near the China-Mongolia border. Its coordinates are approximately 420-440N and 110°-114E(Jiang,1983).The Paleogene strata in the basin are well-exposed and fossiliferous. Since the 1920s, the Cen-tral Asiatic Expeditions of the American Museum of Natural History(CAE), the Sino-Soviet Paleontological Expedition, the Regional Geological Survey of Nei Mongol Autonomous Region, and the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences (in collaboration with the American Museum of Natural History and the Carnegie Museum of Natural History in recent years) have investigated the Erlian Basin. Such work has established a stratigraphic framework and provided the basis for a number of proposed lithostratigraphic unit names. Several faunas from the Erlian Basin ha been the base of Asian Paleogene Land Mammal Ages that have been widely accepted(Luterbacher et al.,2004). The Erlian Basin has thus become an important area for the study of Asian Paleogene mammals, stratigraphy and related issues. For a long time, however, some confusion has existed regarding the usage oflocality names, and clarity has been lacking with respect to the definitions, subdivisions and correlative relationships of some lithostratigraphic units in the region. In the course of his study of Asian Paleogene tapiroids, Radinsky (1964) discussed the Eocene and Oligocene fossil localities in the Erlian Basin and questioned the stratigraphic assignments of some localities, but he failed to clarify the local stratigraphy. The purpose of this paper is to clarify some of the un-certainties that exist regarding both locality names and stratigraphy, based on our recent investigations and on comparisons of our new data with previous references and the CAE archives.