The chemical composition of essential oil extracted from Allium sativum bulbs harvested in the region of El Harrouch in Skikda was studied by gas chromatography coupled with mass spectrometry; six compounds were identified which predominant materials are: methyl allyl trisulfide (34.61�20and diallyl disulfide (31.65� The antibacterial activity was tested on 52 clinical strains and one reference strain of Pseudomonas aeruginosa by both variants of the dilution method, the dilution method in liquid medium and the dilution method in solid medium. The results showed that the essential oil of Allium sativum has an inhibitory activity of growth compared to over 50�0of strains tested with MICs relatively averages between 32 and 128 μg•mL-1.