Ring species and ring diversification provide good evidence of gradual speciation. Studying differentiation in ring species/ring diversification patterns contributes to understanding the process of speciation. We applied a fine-scale phylogeographic survey to two congeneric small mammals, the South China field mouse (Apodemus draco) and the Chevrier’s field mouse (A. chevrieri), which are endemic to the mountains of Southwest China (MSC), combining mitochondrial (Cytb and COI) and nuclear (microsatellite loci) markers, with dense sampling throughout the range (411 A. draco from 21 sites and 191 A. chevrieri from 22 sites), as well as species distribution modeling, scenario testing of dispersal routes and redundancy analyses of environmental and spatial factors to characterize the population genetic structure and infer the proximate formation mechanism of these patterns. Our results revealed that both A. draco and A. chevrieri clustered into western and eastern lineages, which dispersed clockwise and anticlockwise, respectively, from west to northwest. The two species showed gradually increasing genetic differences with geographic distance and displayed a ring diversification pattern around the Sichuan Basin. The tectonic events of the Qinghai-Tibetan Plateau (QTP) and climatic oscillations during the Quaternary triggered the genetic divergence of A. draco and A. chevrieri by providing environmental heterogeneity and spatial variation, and shaped the ring diversification pattern with the effect of species traits. Our report on the two ring patterns provides supportive evidence for the hypothesis that speciation is a continuous process in nature. Key words: small mammal, phylogeography, speciation, ring species, diversification, mountains of Southwest China