Sarmentogenin(Ⅰa) isolated from the crude extract of _{Strophanthus divaracatus} (Lour.)Hook et Arn,by mild acid hydrolysis was dehydrated by (a) further acidic treatment or (b) phosphorus oxychloride-pyridine dehydration via its acetate to β-anhydrosarmentogenin (Ⅲa).The latter was shown to be identical with strophanthiline A previously isolated from the same plant.