Abstract: Iso-Chuanliansu (2), a new constituent, was isolated from Chinese medicine-the bark of Melia toosendan in the province of Sichuan and Melia azedarach in the province of Guangxi. The decoction of the bark of Melia has been used as anthelmintic against ascaris among the people for generations. The molecular formula of iso-Chuanliansu (2) is C₃OH₃₈O₁₁, the same as Chuanliansu (1). It is also a β-substituted furanoid triterpene. The difference between Chuanliansu(1) and iso-Chuanliansu(2) resides only in ring D. The 14β, 15β epoxide group in the former is replaced by a carbonyl group situated at the 15 position in the latter. It is proved by the fact that when Chuanliansu(1) was treated with mineral acid, it could be transformed into iso-Chuanliansu (2) smoothly. The CD curve of iso-chuanliansu(2), similar to that of Amoorastatone (5), showed negative cotton effect at 298, 309 and 316 nm, so that the stereo-pattern may be shown as formula(2). It is a 1α, 7α-dihydroxy-3α, 12α-diacetoxy-11, 15dioxo-19β, 28β-acetal-meliacan.