abstract in algerian traditional medicine, the aerial parts of ammoides atlantica (coss. et dur.) wolf. (apiaceae) are reported to have a wide range of biological activities such as antibacterial and antidiarrheic activity. the in vitro antibacterial activity of the oil was evaluated by disc diffusion method against several strains of bacteria, and this activity was shown to be very strong against most of the tested microorganisms, especially escherichia coli atcc 25922, staphylococcus aureus atcc 25923, and enterococcus faecalis atcc 29212. the mic was also carry out and bacillus subtilis atcc 6633 (vegetative form) resulted to be the most sensitive microorganism with a mic value inferior of 6.25 mg/l. the essential oil was analyzed by gc and gc/ms. the main components were thymol (53.2%), -terpinene (19.4%) and p-cymene (10.6%)