Invasive species tend to pose a threat to ecosystem biodiversity, functioning, and ecosystem service provision. This study was conducted in Burkina Faso to assess the competitiveness of an invasive species Senna obtusifolia that is a less palatable legume plant in West African Sahelian rangelands. To address the research hypothesis that the recurrent drought in the Sahel results in S. obtusifolia being more competitive in the land invasion, we conducted an interspecific competition involving S. obtusifolia and 3 herbaceous species (Andropogon gayanus, Chamaecrista mimosoides, and Pennisetum pedicellatum) in a greenhouse experiment under four water stress regimes using a replacement series design. The height and biomass of each species were measured throughout four months experiment. In the severe water regime, S. obtusifolia was the most sensitive to water deficit while the 3 other species were found to be resistant. In addition, in all water regimes, the aggressivity index revealed that S. obtusifolia was less competitive than the grass species A. gayanus and P. pedicellatum. Further, the study discovered that drought in the Sahel made S. obtusifolia more vulnerable than the other species. Hence the invasion of Sahelian rangelands by S. obtusifolia could be favored by overgrazing that reduces fodder species' dominance and competitiveness. Good management of sahelian rangelands by controlling grazing could help to reduce S. obtusifolia invasion and provide more fodder for livestock.