The essential oil obtained from leaves and stem barks of the Southern Brazilian native Drimys brasiliensis Miers, a tree with medicinal properties, was analyzed by gas chromatography (GC) and GC/mass spectrometry (MS). The oil was characterized by sesquiterpenoids (66%), cyclocolorenone being the most abundant (30.4%), followed by bicyclogermacrene (11.8%) and alpha-gurjunene (6.0%). Laboratory tests were carried out to determine the toxicity of the essential oil on larvae of the cattle tick Rhipicephalus (Boophilus) microplus and the brown dog tick Rhipicephalus sanguineus by the larval immersion test. It was observed that the oil was lethal, killing 100% of the larvae of both ticks at the doses of 25, 12.5, and 6.25 microl/ml. The lowest dose tested, 3.125 microl/ml, was also toxic, killing 95-98% of the larvae.