The taxonomic position of Bobrinski's serotine (Eptesicus bobrinskoi) is still unclear. In the present study the relationships between E. bobrinskoi and other small Palaearctic serotines were examined based on morphometric and molecular evidence. Both mitochondrial (cytochrome b) and nuclear (THY) sequence data indicate that E. bobrinskoi is closely related to Gobi serotine (E. gobiensis). The difference between these two forms is significantly lower than between either of them and any other Palaearctic serotine. The results of morphometric analysis suggest that morphological differentiation between E. gobiensis and E. bobrinskoi is to a large extent accounted for by size difference. It is concluded that the species status of Bobrinski's serotine is doubtful and this bat should be treated as a subspecies of E. gobiensis.