Water distilled essential oil of aerial parts of Tanacetum cadineum (Boiss.) Heywood subsp. orientale Grierson (Asteraceae) was analyzed by GC and GC/MS methods. Ninety three compounds have been characterized representing 97.8% of the oil. 1,8-Cineole (1.8.9%), p-cymene (15.7%), terpinen-4-ol (14.8%), borneol (9.8%) and gamma-terpinene (3.5%) were found to be the major constituents of the oil. Antimicrobial activity of the oil was tested via micro-dilution broth method. Escherichia coli, Staphylococcus aureus, Enterobacter aerogenes, Salmonella typhimurium, Bacillus cereus, Staphylococcus epidemidis, Candida albicans were used as the test microorganisms.