Multi-approach characteristic of Oudemansidium komareki contains the morphological data based on several dozens of larvae along with the first molecular data on the mitochondrial COI and 28S gene obtained for the species. The ectoparasitic mites were collected from Myotis capaccinii (new host record) and Pipistrellus pipistrellus in Romania. A case of multiparasitism of two species of Oudemansidium – O. komareki and O. musca on common pipistrelle (P. pipistrellus) is reported, and complementary data to the knowledge of the morphology of O. musca support a separate identity of both species. The verified diagnoses of O. komareki and O. musca, resulting from widening the knowledge of intraspecific variation, are proposed and the characters that allow differentiating the species presently assigned to Oudemansidium are discussed.