SB-204900 (1), a novel oxirane carboxamide, has been isolated from a hexane extract of the fruit tree Clausena lansium (Rutaceae). The structure of 1 was determined by detailed spectroscopic methods and unambiguously confirmed by a single-crystal X-ray diffraction study. Clausena lansium is a fruit tree found in southern China and cultivated in Taiwan. In traditional medicine its leaves have been used for the treatment of coughs, asthma, and viral hepatitis as well as dermatological and gastrointestinal diseases.1-3 Previous studies3,4 have resulted in the isolation of the cinnamamide derivatives lansamide I and lansiumamides A, B, and C, in addition to related pyrrolidinones.2,5-9 Our investigation of the hexane extract of the leaves from C. lansium (Lour.) Skeels (Rutaceae) has resulted in the isolation of a novel oxirane carboxamide, SB-204900 (1). We report here the structure determination of this novel compound.