the essential oils from cantinoa carpinifolia (benth.) and lippia origanoides (kunth.) were obtained by hydrodistillation. the constituents were determined by gc-ms and gc-fid. the antioxidant activities were evaluated by the abts, dpph and hydroxyl radicals, phosphomolybdenum complex, reducing power, -carotene/linoleic acid and the tbars methods. analysis of variance and the scott-knott test of the means at 5% were performed. the principal constituents in the essential oil from c.carpinifolia were -thujone (32.15%) and -thujone (22.22%), whereas carvacrol (41.51%), p-cymene (18.36%) and -terpinene (17.03%) were obtained from l.origanoides. the respective ic50 for the essential oils from c. carpinifolia and l.origanoides in the abts tests were >1000 and 110 ug ml-1; dpph (110 and >1000 ug ml-1), hydroxyl (636 and 484 ug ml-1), -carotene (>2000 and 215 ug ml-1) and tbars (778 and 527ug ml-1). the l. origanoides essential oil was the most effective antioxidant.