The antimicrobial activity of essential oil and two compounds ,namely Caryophylene and Limonene , isolated from aerial parts of Syrian Inula viscosa(l.) were tested against two gram positive bacteria, (Listeria Monocytogeneses & Staphylococcus Aureus)and two gram negative (Salmonella Typhimurium & Proteus Mirabilis).The results stated that the MIC50 of essential oil were amounted to about 12.5 μl/ml and 6.3 μl/ml for gram positive and negative bacteria respectively ,whereas the MIC50 of Caryophhylene and Limonene were amounted respectively about 50 μl/ml and 25 μl/ml for both gram positive and negative bacteria respectively .