Abstract: Rutaceae Clausena lansium (Lour) Skeels, widely distributed in Southern China, is a kind of fruit tree. The crude extract from its leaves has been used for the treatment of acute and chronic viral hepatitis and its effect of lowering eleveted SGPT level was observed. A cyclic amide, Clausenamide, with novel structure (Ⅰ) possessing the above activity has been isolated in our laboratory from the leaves of C. lansium. By means of spectrometric data combined with chemical reactions, the structure has been elucidated and the proposed structure (Ⅰ) was further confirmed by X-ray diffraction analysis.