A combined approach based on the complex use of molecular, morphological and ecological data has shown that the ‘eastern’ group of forms of transpalearctic Daubenton's bat, Myotis daubentonii (Kuhl, 1817), deserves a status of distinct species, and conforms to M. petax, described by Hollister in 1912 from the Republic of Altai in the south of Western Siberia. In our genetic analysis we used SINEs (short interspersed elements) of nuclear DNA as genetic markers, and by means of Inter-SINE-PCR, have clearly demonstrated a species distinctiveness of M. petax. Our further analysis has also shown, that they considerably differ from M. daubentonii s.str. in skull proportions, dental features, as well as in bacular shape and size. Both species also differ in their ecology and general appearance, especially coloration.