Introduction: Leishmaniasis is one of the neglected tropical diseases, threatening lives of about 350 million people globally. Brucea antidysenterica seeds are used for the treatment of cutaneous leishmaniasis in the traditional medicine in Ethiopia.Objective: This study aimed to evaluate Brucea antidysenterica seeds' anti-leishmanial activity in vitro. Methods: The crude (80% methanol) extract of Brucea antidysenterica seeds and its fractions were evaluated for their antileishmanial activities against promastigotes and intracellular amastigotes of Leishmania donovani and Leishmania aethiopica, and for their cytotoxic effects against mammalian cells. The quantitative estimations of total phenolic compounds (TPCs), flavonoids (TFCs) and alkaloids (TACs) were determined, spectrophotometrically. Median inhibitory concentration (IC 50 ) and median cytotoxic concentration (CC 50 ) of the extract and its solvent fractions were calculated using GraphPad Prism 9.1.0 computer software. Data was presented as mean ± standard error of the mean (SEM). Results: The crude extract and its hexane, ethyl acetate and butanol fractions showed anti-leishmanial activities, with IC 50 values of 4.14-60.12 µg/mL against promastigotes, and 6.16-40.12 µg/mL against amastigotes of both Leishmania species. They showed moderate cytotoxicity against Vero cell lines and peritoneal mice macrophages, with CC 50 values of 100-500 µg/mL, but >1600 µg/mL against red blood cells. Selectivity indices ranged from 7.97 to 30.97. The crude extract, and its ethyl acetate and hexane fractions possessed 54.78-127.72 mg of gallic acid equivalent TPC, 18.30-79.21 mg of quercetin equivalent TFC, and 27.62-97.22 mg of atropine equivalent TAC per gram of extracts. Conclusion:The seeds of the plant possessed anti-leishmanial activities against L. aethiopica and L. donovani that might provide a scientific justification for its use in the treatment of leishmaniasis by traditional healers. Future works are recommended to isolate, purify and identify the possible secondary metabolites attributed to the anti-leishmanial activity.