Abstract The antimicrobial effects of essential oil isolated from Artemisia annua L. were studied against Escherichia coli, Staphylococcus aureus, Streptococcus faecalis, Pseudomonas aeroginosa, Klebsiella pneumonia, Bacillus subtilis, Bacillus licheniformis, Candida albicans and Saccliaromyces cerevisiae. The disc diffusion method was used to evaluate the zone of microbial growth inhibition at various concentrations of the oils. Minimal Inhibitory Concentration (MIC) and Minimal Bactericidal Concentration (MBC) of the oils were determined and compared with each other. The kinetics of microbial destruction by the oil was studied. The oil was found to have antimicrobial particularly antibacterial effect. GC and GC/MS analysis of the oil revealed 17 components. The major components were artemisia ketone (24.2%), Î±-pinene (12.1%), 1,8-cineole (9.8%), camphore (8.4%), Î±-selinene (7.5%) and borneol (6.0%). The high monoterpenes hydrocarbons seem to contribute for strong antimicrobial activity of A. annua.