Mount Nimba, covering 674 km², straddles Liberia, Guinea and Côte d'Ivoire (Ivory Coast) in West Africa and is situated in the transition zone between the tropical forest zone to the south and moist woodlands to the north. Mount Nimba supports an exceptional biodiversity, with a number of endemic plants, invertebrates and vertebrates restricted to the massif, including the bat Hipposideros lamottei. Previous surveys suggested a high bat richness of 41 species associated with the mountain. During a series of surveys conducted in 2008–2012, we found that the bat diversity in this region far surpasses earlier figures and currently is 59 species. At least one bat species is entirely restricted to the mountain, with several other near-endemics or Upper Guinea forest endemics. Three species are listed as threatened by the IUCN, including one Critically Endangered. Furthermore, the conservation statuses of nine taxa have yet to be evaluated by the IUCN, several of which are recently described species and are likely to be threatened. This study highlights the irreplaceability of Mount Nimba for the conservation of bat diversity on the African continent, and draws attention to its protection.