The chemical composition of the essential oil of Artemisia annua L. was determined by GC/MS analysis. Among the thirty-seven constituents found, camphor (31.7 %), artemisia ketone (22.3 %), 1,8-cincole (10.1 %), caryophyllene oxide (7.1 %), alpha-copaene (3.4 %) and camphene (3-3 %) were the major components. The in vitro antifungal activity of the essential oil was evaluated against economically important foliar and soil-borne fungal pathogens of tomato, including Sclerotinia sclerotiorum, Botrytis cinerea, Phytophthora infestans and Verticillium dahliae. Both contact and volatile phase effects of different concentrations of the essential oil were determined by using two different methods. Amongst the fungal isolate, S. sclerotiorum was found to be highly sensitive to volatile and contact phase of the essential oil. Minimum fungicidal concentrations of the volatile phase of the essential oil for S. sclerotiorum, B. cinerea, P. infestans and V. dahliae were 1.6, 2.4, 2.4 and 4.4 mu g/ml air, respectively. The essential oil in the contact phase showed minimum fungicidal concentration ranging from 6.4 mu g/ ml to 51.2 mu g/ml. Volatile and contact phase of the essential oils, at 2.4 and 51.2 mu g/ml concentrations, were found to completely inhibit the conidial germination and germ tube elongation of both fungal pathogen tested.