Abstract: The Shanwang Stage, a chronostratigraphic unit of the Chinese Neogene, corresponds to the Shanwang Mammal Age (Deng, 2002). The defined biostratigraphic zones of the Shanwang Stage correspond to MN3 ～ MN5 of the European mammal ages , and its lower boundary should be at 2015 Ma according to the paleomagnetic dating of the lower boundary of MN3 (Steininger, 1999) . On the basis of the principles of the modern stratigraphy for the stage establishment, the Shanwang Formation is studied on the biostratigraphy and dated by paleomagnetic and isotopic methods. The new dating indicates that the lower boundary of the Shanwang Formation is at 18 Ma. As a result, the age of the Shanwang mammalian fauna is advanced to correspond to MN4 of the European mammal ages from MN5 in the traditional viewpoint (Qiu et al., 1999). Actually, Qiu et al. (1985a, 1985b, 1991) considered that Palaeomeryx tricornis, Ursavus orientalis, Thaumastocyoninae gen. et sp. indet., and Plesiotapirus yagii from the Shanwang fauna should imply an age corresponding to MN4. Liu et al. (2002) indicated that Hyotherium penisulus of the Shanwang fauna should be referred into Listriodontinae, and it has the same age with MN4, the earliest appearance of this subfamily. On the other hand, the mammalian fauna corresponding to MN3 in the lower part of the defined Shanwang Stage is still absent on the section of the Shanwang Formation. There are no deposits of the early Shanwang Age from 20. 5 Ma to 18 Ma so that the lower boundary of the Shanwang Stage cannot be found in the Shanwang section. International Stratigraphic Guide advocates basically determing the lower boundary2stratotype in order to establish a chronostratigraphic unit, and its upper boundary should be determined by the lower boundary of its overlying unit (Salvador, 1994). In the Lanzhou Basin and Qin’an Area of Gansu Province, the thick deposits from the Oligocene to the Miocene are well exposed, with the mammalian fossils of the lower part of the Shanwang Stage and fit deposits for the paleomagnetic dating (Qiu et al., 1997; Guo et al., 2002). Consequently, they are favorable localities to establish the lower boundary2stratotype of the Shanwang Stage.