Four steroidal saponins were isolated from the leaves of Yucca de-smetiana Baker. Their structures were established using one- and two- dimensional NMR spectroscopy and mass spectrometry. The structure of the new steroidal saponin was identified as: (25R)-3b-hydroxy-5 a-spirostan-3-O-b-D-xylopyranosyl-(1 ? 2)-b-D-galactopyranosyl-(1 ? 2)-O-[b-D-glucopyranosyl-(1 ? 3)]-b-D-glucopyranosyl-(1 ? 4)-b-D-galactopyranoside (desmettianoside C) along with three known spirostanol and furostanol saponins. The isolated saponins were evaluated for their antitumor activity against HCT116, MCF7, HepG2, and A549 cell lines. Saponins 3 and 4 showed potent activity against HCT116, MCF7, and HepG2 cell lines in comparison with the positive control doxorubicin. A molecular modeling approach was performed to establish conformational criteria that could affect the biological activity of the isolated saponins.