Triterpenoid compounds from the petroleum ether extracts of Marsdenia formosana MASAMUNE (Asclepiadaceae) were examined. The known triterpenoids, α-amyrin (I), α-amyrin acetate (II), α-amyrenone (III), α-amyrin cinnamate (IV), neoilexonol acetate (VI), lupeol (VII), lupenyl acetate (VIII), and lupenone (IX) were isolated and characterized. In addition to these known compounds, three new triterpenoids, one of which was named marsformol (XII), were also isolated. Structures (V, X, and XII) of these new triterpenoids were assigned from chemical and spectral data.