Official Development Assistance is a major funding source for biodiversity conservation in developing countries, and it is therefore important to understand the effectiveness of biodiversity aid. However, three challenges hamper the analysis of how effectively biodiversity-related development aid (biodiversity aid) contributes to the conservation of biodiversity and its sustainable use. First, few indicators measure biodiversity aspects at country level in a consistent and comparable way. Second, biodiversity aid reporting methods do not reveal the exact funding amount for projects’ biodiversity component. Third, changes in biodiversity status are empirically and conceptually difficult to attribute to aid activities. Based on a theoretical elaboration of these challenges, we argue that for a better assessment of how biodiversity aid contributes to conserving biodiversity and to reducing biodiversity loss, three improvements are required: a more frequent and more consistent assessment of the biodiversity status across countries, more exact quantification of biodiversity aid, and a more detailed understanding about biodiversity loss and the role biodiversity aid plays. These improvements will allow for more reliable aid-effectiveness analyses, which will, in turn, enable better informed aid-allocation decisions to be made.