The essential oils of Zataria multiflora (Labiatae) from four regions of Iran were investigated by GLC and GC-MS methods. The main constituents were carvacrol, thymol, linalool and p-cymene. The percentage of the constituents (in dry and wet plant) of different regions have been compared. Antibacterial and antifungal effects of these essential oils have been studied. The essential oil with highest percentage of thymol and carvacrol had a significant antimicrobial activity.