The karyotype of Mustela kathiah was first described. Its structure is most similar to the karyotype of M. altaica, differing inthe morphological peculiarites of five pairs of large chromosomes. A comparative analysis of mitochondrial genes in the species Mustela allowed us to clarify understanding of the place of M. kathiah in the system of the genus. The earlier hypothesized proximity of the species to a group of small weasels (altaica, nivalis) or to a group of South Asian species (strigidorsa, nudipes) was not confirmed. A high level of differences between M. kathiah of Vietnam and specimens from southern China in nucleotide sequences of the cytochrome b (7.7%) and ND2 (6-6.2%) genes was found. Perhaps these differences, manifested in populations of M. kathiah from different regions, are adaptive.