A new bisdesmosidic spirostanol saponin, along with three known saponins, were isolated from Agave americana (Agavaceae). The structure of the new saponin was elucidated as (25R)-3 beta,6 alpha-dihydroxy-5 alpha-spirostan-12-one 3,6-di-O-beta-D-glucopyranoside. Among the isolated saponins, hecogenin tetraglycoside showed cytotoxic activity against HL-60 human promyelocytic leukemia cells with an IC50 value of 4.3 micrograms/mL.