The Eastern Arc Mountains of East Africa are known for an exceptionally rich flora and fauna with very high endemism. For the conservation of rare forest birds these mountains are of the utmost importance in Africa. We provide the first population estimate of the endemic Loveridge's Sunbird Nectarinia loveridgei in the Uluguru Mountains of eastern Tanzania. Our study was conducted between September and December 2000. Capture-recapture using mistnets was used to gather data at eleven study sites between 1,300–2,600 m altitude in four different areas of the Ulugurus. The program CAPTURE was used to estimate the population at each study site. Since the home range of Loveridge's Sunbird is unknown, the density of the potential population was calculated by assuming home ranges ranging from 0 km2 through to 3 km2. When combined with data on the forest area in the Ulugurus and fixing the lower and upper home range sizes for this species at 0.1 km2 and 0.8 km2, we obtain an estimated total population ranging from 21,000 to 166,000 individuals. A median home range of 0.45 km2 estimates the population close to 37,000 individuals. The species does not seem threatened but its long-term survival will depend on the survival of the forest, and in particular on how well the forest reserves on the Ulugurus are managed in the future.