A new subspecies of the least weasel, Mustela nivalis (Mammalia, Carnivora) was described from the central mountains of Taiwan. The external and skull morphology, and conventional, G-banded and C-banded karyotypes of the present subspecies were compared with those of other subspecies. This new subspecies is distinct from the other subspecies by relatively longer tail, a broad and short interorbital region, short and narrow rostrum, anteriorly positioned infraorbital foramen, well developed protocone and parastyle of the fourth upper premolars, and anterior margin of right and left upper molars located in a straight line. The number of C-blocks in chromosomes of this new subspecies is less than those for other M. nivalis subspecies.