The analysis and identification of essential oils hydrodistilated from an endemic species of Algeria (Genista microcephala) by means of gas chromatography and mass spectroscopy was realized in this investigation. In addition, their antagonistic activity against some pathogenic bacteria was screened. Acceptable yield, 0.20% is obtained. 27 compounds were identified, representing 98.9% of the total essential oil. The analysis showed that the main constituents of the essential oils are the fatty acid. The major compound was palmitic acid (29.6%), other components present in appreciable contents were: lauric acid (21.5%), myristic acid (8.7) and linoleic acid (2.5%). The effects of these oils on the growth of Escherichia coli (ATCC 25922), Pseudomonas aeruginosa (ATCC 27853) and Staphylococcus aureus (ATCC 25923) were investigated by the diffusion method. The oils showed significant antibacterial activities.