The aerial part of Artemisia iwayomogi KITAMURA has traditionally been used for antitumour, immunomodulating, antimutagenic, antioxidant, antibacterial, antifungal, antipyretic, diuretic, liver protective effect, and choleretic purposes in Korea. The chemical composition of the essential oil obtained from A. iwayomogi was analyzed by GC/MS. The essential oil and its major compounds were tested for antibacterial activities against 15 different genera of oral bacteria. The essential oil of A. iwayomogi was rich in camphor (17.96%), 1,8-cineole (14.79%), terpinen-4-o1 (3.28%), ${alpha}-terpineol$ (17.60%), and ${eta}-caryophyllene$ (4.05%). The essential oil of A. iwayomogi exhibited considerable inhibitory effects against all obligate anaerobic bacteria (MICs, 0.05 to 0.2 mg/ml; MBCs, 0.1 to 0.4 mg/ml) tested, while its major compounds demonstrated various degrees of growth inhibition.