Abstract We investigated the chemical composition and the antibacterial activity of the essential oils of two populations of Thymus numidicus Poiret. differentiated by the color of the flowers. Forty-two compounds were identified by gas chromatography (GC) and gas chromatography/mass spectrometry (GC/MS), representing more than 97% of the oil. The main components of both oils were thymol (59.0%, 68.0%), Î³-terpinene (8.5%, 4.2%), p-cymene (5.8%, 4.5%), carvacrol (3.7%, 4.2%) and Î±-pinene (5.3%, 3.5%) (purplish-white and violet varieties, respectively). The oils exhibited promising activity in the disc diffusion antibacterial assay.