The Atacora Mountain range is an important mountain chain in the West African landscape. It extends from northern Benin to Togo and Ghana. More and more cattle are starting to graze on the Beninese part of this range, although there is a critical lack of basic data on its ecological function. The present study assesses the effects of topography and aspect on the grassland biomass production of these mountains. The results show that annual grassland biomass production averages 5.29 tonnes dry matter (DM)/ha. This biomass production is significantly impacted by aspect (east facing versus west facing). Biomass is lower on east-facing sides (4.97 tonnes DM/ha) than on west-facing sides (6.10 tonnes DM/ha) and hilltops and valleys (6.24 tonnes DM/ha). This effect may be explained by direct exposure of east-facing sides to the harmattan, a northeast dry wind blowing from the Sahara Desert. No significant impact of topography on biomass production is observed.