Abstract: This paper deals with an assemblage of small mammals collected from the upper Youshashan Formation at Shengou, Delingha, Qinghai Province during the field seasons of 2002−2005. The Shengou micromammalian fauna is composed of 16 species from 12 families belonging to the orders Insectivora, Rodentia and Lagomorpha. It is the most diverse and abundant micromammalian fauna known from the vast Qinghai-Xizang Plateau. One species of Muridae (Huerzelerimys exiguus) is described as new, and represents a new record of the genus in China. The Shengou Fauna appears to closely resemble the assemblage from the lower part of the Bahe Formation of Shaanxi, but slightly younger than the latter. It is most probably attributable to early Late Miocene, or the early Baodean of the Chinese Land Mammal Ages, correlated, in European terms, with late MN10 or early MN11. The fauna reflects a faunal distribution of the modern temperate region in China, and suggests a dry and open environment. Nevertheless, the climate in Qaidam area was unlike the exact situation of the present day, but was less arid with more vegetation during the early Late Miocene than it is today. Both habitats and composition of the fauna may imply that the Qinghai-Xizang Plateau had undergone a definite uplift in relation to the loess plateau after Miocene.