Two glycosides have been isolated from Astragalus membranareus var. mongholicus, and their structures have been determined to be 3-O-β-D-xylopyranosyl-25-O-β-D-glucopyranosyl-cycloastragenol and (3R)-(-)-7,2'-dihydroxy-3',4'-dimethylisoflavan-7-O-β-D-glucopyranoside by spectroscopic means and chemical transformations. Astragalus membranaceus Bge. var. mongholicus (Bge.) Hsiao (Leguminosae) is a medicinal plant frequently used as a traditional medicine in China, Japan, Korea, and Southeast Asia. It has been reported to strengthen superficial resistance and to promote the discharge of pus and the growth of new tissue. The crude extract has shown significant antiviral and immunostimulant activities and inhibits the activities of murine retroviral reverse transcriptase and human DNA polymerases. Previous studies of chemical constituents from this species have resulted in the isolation of saponins, flavonoids, polysaccharides, free amino acids, and an isoflavan glycoside. During our study of the polar constituents, we have isolated a new saponin, isoastragaloside IV, which is an isomer of the previously reported astragaloside IV, together with an isoflavan glycoside 5 from the n-BuOH-soluble portion of the EtOH extract. In this paper, we report the isolation and structure elucidation by spectroscopic means and chemical transformation of these two compounds.