The study reports for the first time the chemical composition and the antibacterial activity of the essential oil hydrodistilled from three Cistaceae growing in Algeria: Cistus ladaniferus L., C. albidus L. and C. monspeliensis L. The oils were analyzed by GC-FID and GC-MS analyses. The major components of C. ladaniferus were 5-epi-7-epi-α-eudesmol (13.6%) and borneol (12.5%) whereas for C. albidus the main constituents were epi-α-bisabolol (11.4%) and β-bourbonene (8.7%). Epi-13-manoyl oxide (28.6%), kaur-16-ene (8.1%) and nonanal (5.4%) were the principal ones for C. monspeliensis. In vitro, antimicrobial activity of the oils was investigated against nine microorganisms by disk diffusion and agar dilution assays. The Gram-positive bacteria resulted sensitive to the three oils, especially Bacillus subtilis ATCC 6633 and Staphylococcus aureus ATCC 25923. The volatiles of C. monspeliensis showed the best activity compared with other oils, comparable to or better than Gentamicin, a conventional antibiotic used as positive control in this study. The minimum inhibitory concentration (MIC) value of the oil was 0.25μg/L
