Abstract The composition of the essential oil of the aerial parts of Artemisia lobelii during four stages of the growing cycle (full foliation stage, pre-bloom, full bloom and post-bloom stage; between June and October) were studied by GC/MS. The major constituents of the oil were camphor (33.2-36.8%), 1,8âcineole (15.2-21.1%) and artemisia ketone (6.0-24.2%). The antimicrobial activity of oil against Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa and Staphylococcus aureus was investigated. It was found that the oil showed strong activity against Pseudomonas aeruginosa.