Niviventer andersoni (Thomas, 1911) is an endemic species of China. This taxon has the largest body-size when compared with congeneric species of the genus Niviventer Marshall, 1976. Fossil records showed this species extended to the low altitude regions of Southeast China during the late Quaternary in Chongqing and Guizhou, suggesting its potentiality of southward expansion during the cold climate. However, historical resources suggested that N. andersoni is mainly confined to the Southwestern mountainous region in China. A comprehensive study on its morphological differentiation is also lacking. Our study is intended to explore the intraspecific morphological variation among different populations and revise the distribution range of this species by integrating information from collection records, DNA sequences, and morphological data. Our databases were derived from specimens preserved in major zoological museums of the world, field work carried out in the last ten years, and fossil records compiled from all available historical publications. Phylogenetic structure analyses based on Cytochrome b displayed three genetic lineages within this species. N. andersoni andersoni is included in the lineage of Mountains around Sichuan Basin and Southeast and Central China, N. a. ailaoshanensis is included in the lineage of Southwest Yunnan and Southeast Tibet. Based on statistical

analyses of craniodental measurements, significant morphological variation was presented beween different geographical populations of N. andersoni. Molecular voucher specimens and museum collections showed that N. andersoni is widely distributed in Central and Southern China, including southeastern Tibet region to the Hengduan Mountains, Qinling Mountains, and the southeast Wuling Mountains. However, when compared with the elevation of fossil sites, the distribution of extant populations showed clear trend of upward shift.