Abstract The essential oil of the aerial parts of Ophryosporus heptanthus (Asteraceae) from Bolivia was analyzed by GC and GC/MS. The oil was characterized by a high percentage of santolinatriene (â¼ 47%) and the presence of precocene II (â¼ 8%) as the most important minor constituent. The other compounds were monoterpenes (â¼ 16%), with p-cymene as the major compound (â¼ 4.8%), sesquiterpenes (â¼ 6%), oxygenated sesquiterpenes (â¼ 8%) and oxygenated monoterpenes (â¼ 4.5%). Key Word Index: Ophryosporus heptanthus Asteraceaeessential oil compositionsantolinatriene6,7-dimethoxy-2,2-(2H)-benzopyranprecocene II