A novel sesquiterpene lactone, pseudomajucin (1) was isolated from the pericarps of Illicium majus, a Chinese Illicium plant, together with its glucoside (2). The structure elucidation of 1 was performed by the spectroscopic method, and finally by and X-ray crystallographic analysis. Interestingly, the structure of pseudomajucin resembled that of the lactone compound which was afforded by treatment of pseudoanisatin with a basic medium. The glucosidic linkage position in the structure of 2 was determined as C-7 in that of 1 by the spectroscopic analysis of 2 and its acetate.