Abstract A comparison of the chemical composition and antibacterial activity of the essential oils obtained from the aerial parts of Semenovia dichotoma (Boiss.) Manden. (which is endemic to Iran), Johreniopsis seseloides (C.A.Mey.) M.Pimen., and Bunium cylindricum (Boiss. et Hohen.) Drude were carried out. The oils were obtained by water-distillation and were analyzed by GC and GC/MS. Caryophyllene oxide (25.5%) and β-pinene (10.9%) were the main components in the oil of S. dichotoma. The oil of J. seseloides was found to contain β-pinene (14.9%) and germacrene D (11.1%) as the major constituents. The major components found in the oil of B. cylindricum were myristicin (43.1%), β-phel-landrene (20.0%), β-pinene (15.6%) and α-pinene (10.7%). Antibacterial activity was determined by measurement of growth inhibitory zone.