en شیمی دارویی Medical Chemistry پژوهشي Original Research <div style="text-align: justify;"><strong>Background</strong>: The antimicrobial activity of plants has long been considered an effective mechanism for controlling pathogenic microorganisms.<br> Objectives: This study aimed to identify phytochemical compounds of the seed extracts from ethnomedicinal plants of <em>Pistacia atlantica</em>, <em>Cassia absus</em>, and <em>Quercus persica</em> with Gas Chromatography-Mass Spectrometry (GC-MS) and investigation of their antibacterial and antioxidant activities.<br> <strong>Methods:</strong> The seeds were collected from Lorestan Province, Iran. Their antibacterial and anti-radical activities were analyzed by disk-diffusion and 2,2-diphenyl-1-picrylhydrazyl assays, respectively. Ethanol (96%), methanol (80%), and distilled water extracts were obtained by the maceration method. The methanol extract was used for the analysis of chemical compositions.<br> <strong>Results:</strong> About 40, 31, and 8 compounds were identified by GC-MS in the seeds of <em>C. absus</em>, <em>P. atlantica</em>, and <em>Q. persica</em>, respectively. Results indicated that 2,4-di-tert-butylphenol (36.043%) and tetradecanoic acid (4.92%) were dominated in the seed extracts of <em>C. absus</em>. However, germacyclopetene (38.119%) and 1,2,3-benzenetriol (8.115%) were dominated in the seed extracts of <em>P. atlantica</em>. Furthermore, 5H-tetrazole-5-thione, 1,4-dihydro-1,4-dimethy (38.505%), and tetradecanoic acid (30.546%) were dominated in the seed extracts of <em>Q. persica</em>. The highest inhibitory activity against <em>Micrococcus luteus</em> was observed on the methanol extract of <em>C. absus</em> with ascorbic acid. A significant difference was observed between the Inhibitory Concentration (IC50) values of methanol extract of <em>C. absus </em>with ascorbic acid.<br> <strong>Conclusion:</strong> Because of the presence of antimicrobial compounds in the tested ethnomedicinal plants, they can be used to synthesize new antimicrobial drugs in medicinal and pharmaceutical sciences.</div> Gas Chromatography-Mass Spectrometry (GC/MS), Cassia absus, Pistacia atlantica, Quercus persica, Infectious bacteria 105 114 http://pbr.mazums.ac.ir/browse.php?a_code=A-10-800-1&slc_lang=en&sid=1 Mostafa Alamholo mostafaalamholo@yahoo.com 10031947532846006626 10031947532846006626 Yes Department of Biotechnology, Institute of Science and Modern Technology, Rojava University, Qamishlo, Syria. Yosof Amraie yosofamraie@gmail.com 10031947532846006627 10031947532846006627 No Department of Plant Biotechnology, Faculty of Agriculture, Bu-Ali Sina University, Hamadan, Iran.