Yield, chemical composition and antibacterial properties of the essential oil extracted from Rosmarinus officinalis in the region of Taza (Morocco) were studied. The average content of essential oil from the leaves of this species is 0.86% relative to the dry matter. Thirty-seven compounds were identified by GC / MS. The Dimenthol (38.83%), the Campholène aldehyde (16.02%), the α-pinene (11.05%), and borneol (10%) are the major chemical compounds of Rosmarinus oil. Strong inhibitory activity against eight pathogenic microorganisms tested was recorded.