An extract of the leaves of Yucca smalliana Fern. (Agavaceae) showed potential antimicrobial activity. Employing a bioassay linked fractionation method, one of the active principles, namely yuccalan, was isolated as a new stroidal saponin. Thn structure of the new steroidal saponin was elucidated as 3-0-${eta}$-D-glucopyranosyl-(1${longrightarrow}$6)-${eta}$-D-glucopyranosyl-(3${eta}$, 5${alpha}$, 6${alpha}$, 25S)-spirostan-3,6,27-triol (1) using various spectroscopic techniques, including IR, MS, ID and 2D $^1$H-NMR, and $^{13}$C-NMR. The purified yuccalan showed antifungal activities against both Rhizoctonia silani and Fusarium oxysporum.