Ultra-Violet (UV) fluorescence has been observed and reported in a wide range of living organisms from lower plants to mammals. In animals, its function has been attributed to a range of behaviours including signalling in mate selection, camouflage, and mimicry, but in many cases its function is unclear, and it may be non-adaptive. Here we report on full pelage UV fluorescence in both Rhinolophus hipposideros, the lesser horseshoe bat and R. blasii, Blasius's horseshoe bat but it is restricted to just these two species within the European Rhinolophidae. The fluorescence in R hipposideros was only observed in adult bats of both sexes and not in juveniles (at least until they were six months old). It is unlikely this phenomenon has any function in the ecology or behaviour of either the species, as rhinolophids lack the short wavelength opsins in their cones to detect light emitted at these wavelengths. It may be maladaptive, as some nocturnal predators may have the ability to detect the fluorescence. Potentially, the differing responses of adults and juveniles have uses in the monitoring of species, especially concerning confirming maternity colonies and estimates of the productivity of colonies. In the case of R. blasii, it may also aid in the identification of this cryptic species that often roosts with other medium-sized horseshoe bats.