Two new sesquiterpene lactones showing moderate antimicrobial activity have been isolated from the root bark of Ceiba pentandra (Bombacaceae) in addition to the known compounds 8-formyl-7-hydroxy-5-isopropyl-2-methoxyl-3-methyl-1,4-naphthaquinone [1], and 7-hydroxycadalene [2]. The new compounds were characterized as 2,7-dimethoxy-5-isopropyl-3-methyl-8,1-naphthalene carbolactone [3] and 2-hydroxy-5-isopropyl-7-methoxy-3-methyl-8,1-naphthalene carbolactone [4] by chemical and spectroscopic studies.