Background: Leishmaniasis is a vector-borne neglected tropical disease caused by Leishmania parasites. Few drugs available to treat the disease are expensive, have toxicity, and resistance to the drugs is emerging. The leaves of Clematis simensis Fresen are one of the Ethiopian medicinal plants commonly used to treat leishmaniasis, but scientific evidence is not yet available. The current study investigates anti-leishmanial activity and cytotoxicity profiles of methanol extract of Clematis simensis Fresen leaves and its solvent fractions. Methods: Clematis simensis Fresen leaves were extracted using methanol through the maceration technique. The anti-amastigote and anti-promastigote potentials of the crude extract and solvent fractions against L. aethiopica and L. donovani were determined by biological assay. Anti-Leishmanial activity (IC50) and median cytotoxic concentration (CC50) for the cytotoxicity assay on the mouse macrophage were calculated from sigmoidal dose-response inhibition curves using the computer software Graph Pad Prism 9.5.0. Amphotericin B was used as a positive control, while dimethyl sulfoxide was used as a vehicle. Result: The methanol extract of clematis simensis Fresen leaves and its hexane, chloroform, and aqueous fractions showed anti-leishmanial activities with IC50 values of 4.385±0.603 to 24.11±2.54µg/ml against promastigotes and 3.67±0.6155 to 90.19±17.68µg/ml against axenic amastigotes of both Leishmania species. They showed moderate cytotoxicity against mouse peritoneal macrophages with CC50 values ranging from 65.045±20.85 to 157.245±100.26µg/ml. The selectivity index towards Leishmania parasites was 1.74 to 66.5µg/ml. The antileishmanial activities could be related to the presence of secondary metabolites like phenolic compounds, alkaloids, and flavonoids. Conclusion: Clematis simensis leaf extracts have shown promising antileishmanial activities, and further isolation of the most active compounds and establishment of the mechanism of action is warranted. In vivo, safety and effectiveness studies are also required