From the fresh rhizomes of Dioscorea deltoidea Wall var. orbiculata , a novel ergostanol saponin, orbiculatoside A ( 1 ), was isolated and identified as 3- O - β- d -glucopyranosyl-ergost-5-ene-3 β, 26-diol-26- O - β- d -glucopyranosyl(1 →3)-[ β- d -glucopyranosyl(1 →2)- β- d -glucupyranosyl(1 →6)]- β- d -glucopyranoside by various NMR techniques in combination with chemical methods. The new saponin showed strong activity against Pyricularia oryzae , with a MMDC (minimum morphological deformation concentration) value of 28.04 μmol/l and was cytotoxic to cancer cell line K562, HCT-15, A549, HT1080, and A2780a in vitro .