Abstract: A new pregnane glycoside,marsdeoreophiside B was isolated from the stems of Marsdenia oreophila(Asclepiadeaece).The structure was elucidated by means of chemical and spec-trometric analysis as 12-O-cinnamyldihydrosarcostin-3-O-β-D-glucopyranosyl(1→4)-O-3-O-methyl-6-deoxy-β-D-allopyranosyl(1→4)-O-β-D-oleandropyranosyl(1→4)-O-β-D-cymaropyranoside.Itshowed significant antifertility activity in rats.