The essential oil composition of Peumus boldus and Drimys winterii was analyzed by means of capillary GC-FID and GC-MS. More than 96% of the total oil components (43 and 54 compounds, respectively) were identified, with ascaridole (51.17 +/- 9.51), p-cymene (16.31 +/- 2.52) and 1,8-cineole (14.45 +/- 2.99) as the main compounds in P. boldus and gamma-eudesmol (21.65 +/- 0.41), followed of elemol (12.03 +/- 0.34) and terpinen-4-ol (11.56 +/- 1.06) in D. winterii. The herbicidal activity was tested against Amaranthus hybridus and Portulaca oleracea. P. boldus essential oil was the most phytotoxic against both weeds, inhibiting seed germination and seedling growth at all concentrations assayed (0.125-1 mu L/mL). D. winterii essential oil did not show any effect on A. hybridus germination and only affected P. oleracea germination at the highest concentration. The results suggest the possible use of the essential oil from P. boldus as a natural herbicide.