en Microbial pathogenesis Microbial pathogenesis Original article Original article <strong>Introduction:</strong> The members of the genus<em> Tanacetum</em> are important medicinal plants. This study investigated the chemical composition and antibacterial activity of <em>Tanacetum lingulatum </em>and<em> Tanacetum polycephalum</em> essential oils on human infectious bacteria. <strong>Methods</strong>: The aerial part of two plants were collected from Urmia Province, Iran. The essential oils were extracted using a Clevenger device. The antibacterial effect of essential oils was determined using the disc diffusion assay, minimum inhibitory concentration (MIC), and minimum bactericidal concentration (MBC) by serial dilution method. Also, free radical scavenging activity by 2,2-diphenyl-1-picrylhydrazyl (DPPH) was examined. Chemical composition was measured using the Gas Chromatography-Mass Spectrometry (GCMS). <strong>Results:</strong> The major constituents in <em>T. polycephalum</em> and <em>T. lingulatum</em> essential oils were 1,8- cineole and camphor, respectively. The highest sensitivity (MIC of 0.312 &mu;g mL^-<span dir="RTL">(</span> was observed with <em>T. polycephalum </em>against<em> Bacillus subtilis. </em>The lowest IC50 (most potent radical scavenging activity) belonged to <em>T. lingulatum</em> essential oil. <em>Pseudomonas </em><em>aeruginosa </em>and<em> Streptococcus pyogenes </em>showed resistance to <em>T. lingulatum</em> essential oil. <strong>Conclusion:</strong> The essential oil of <em>T. polycephalum</em> and <em>T. lingulatum</em> are potential natural antibacterials to treat human pathogenic bacteria and can be used as alternatives to produce antimicrobial agents.<br> &nbsp; Tanacetum genus, Infectious bacteria, Phytochemical 24 29 http://jommid.pasteur.ac.ir/browse.php?a_code=A-10-253-2&slc_lang=en&sid=1 Mostafa Alamholo mostafaalamholo@yahoo.com 0000-0003-1644-8179 Yes Department of Biotechnology, Institute of Science and Modern Technology, Rojava University, Qamishlo, Syria