en پژوهشي Research Article Chemical compositions, antioxidant and antibacterial activities of Zanthoxylum armatum essential oil was analyzed. A total of 3 samples (500 g/each) were collected 6:00 am; 12:00 noon; and 6:00 pm in the same day. The essential oil was extracted by hydro distillation in Clevenger apparatus and their chemical compositions were determined by the GC-MS system. The eleven most abundant ingredients were bornyl acetate (16.61-22.66%), cymene (8.25-12.50%), ?-copaene (7.54-7.59%), ?-terpinene (5.33-7.66%), camphene (4.32-4.66%), limonene (2.66-4.68%), linalool (3.28-3.58%), ?-ocimene (3.24-3.36%), trans -caryophyllene (2.54-3.46%), ?-terpinolene (2.32-3.36%) and germacrene (2.02-2.85%). Antioxidant activity was examined by 2,2'-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging method. Ascorbic acid was used as standard. Essential oil exhibited significant antioxidant activity. The IC 50 of the oil was found 27.0± 0.1 ?g/ml and that of ascorbic acid 15.0± 0.5 ?g/ml. Essential oil of Z. armatum also exhibited moderate antibacterial activity. The results showed that the gram-positive bacteria are more sensitivity to the essential oil than gram negative bacteria. 68 0 http://ijpt.iums.ac.ir/browse.php?a_code=A-10-100-253&slc_lang=en&sid=1 Jagmohan S Negi 1003194753284600851 1003194753284600851 No V.K. Bisht 1003194753284600852 1003194753284600852 No A.K. Bhandari 1003194753284600853 1003194753284600853 No R. Bisht 1003194753284600854 1003194753284600854 No S. Kandari Negi 1003194753284600855 1003194753284600855 No