Long-eared bats of the genus Plecotus are known to occur predominantly in the Palaearctic Region, and at the margins of the Afrotropical and Indomalayan regions. In 2014, four specimens of the genus Plecotus were collected in a high altitude montane temperate forest in the Hoang Lien National Park, northern Vietnam, representing the first record of Plecotus from the Indochinese subregion, and considerably extending the southern border of the genus' distribution range. Detailed morphological comparisons and phylogenetic reconstructions based on the mitochondrial control region suggest that these specimens can be assigned to P. homochrous, a mountain-dwelling bat from the Himalayas. Moreover, for the first time, we provide information on the species' echolocation call and karyological characteristics. Our results also indicate that the taxonomic status of some Plecotus species recognized by previous studies is doubtful and must be revised. Although rarely encountered, Plecotus is likely to be widely distributed at the higher elevations of the Himalayan chain in southern China and the adjoining northern areas of Vietnam, Laos, and Myanmar. Our findings strongly support the importance of the mountainous areas within the Indo-Burma biodiversity hotspot.