Alliums are rich sources of steroidal saponins, flavonoids, and sulphoric compounds of which steroidal saponins have recently received more attention due to their important pharmacological activities. Allium paradoxum L. is a common edible vegetable in north regions of Iran, especially in Mazandaran province, where it is named “Alezi” and considerably used as a raw vegetable, to make dishes, and as a medicinal plant. Phytochemical investigation of chloroform-methanol extract of the plant resulted in the isolation and identification of a dioscin related steroidal saponin, using comprehensive spectroscopic methods including 1D and 2D NMR, its chemical structure was determined as (25R)-spirost-5-en-3b-ol,3-O-α-rhamnopyranosyl-(1→4)-α-rhamnopyranosyl-(1→4)-[a-rhamnopyranosyl-(1→2)]-glucopyranoside. Investigation of in vitro antileishmanial activity of the isolated compound, in 10 and 50 µg/mL concentrations, exhibited significant leishmanicidal effects (P