Abstract A water-distilled oil obtained from the aerial parts of Xanthium brasilicum Vellozo was analyzed by GC/MS. The oil consisted mainly of monoterpenes and a small percentage of sesquiterpenes. Fifteen compounds were identified, of which borneol (28.9%), fenchone (21.1%) and isobornyl acetate (9.1%) were the major constituents. Key Word Index: Xanthium brasilicum Compositaeessential oil compositionborneolfenchone