en ترکیبات طبیعی Natural products پژوهشي Original Research <p>The genus <em>Helichrysum</em> (Asteraceae) is comprised of approximately 500-600 species and used for the treatment of a variety of pathological conditions in folk medicine in many countries. In this study, antioxidant activities of aerial parts of <em>H. pseudoplicatum </em>were investigated employing various <em>in vitro</em> assay systems, i.e. 2,2-diphenyl-1-picrylhydrazyl (DPPH)&nbsp; and nitric oxide radical scavenging, reducing power and hydrogen peroxide scavenging. IC₅₀ for DPPH radical-scavenging activity was 438.9 &plusmn; 15.6 &micro;g/ml. The extract exhibited good reducing power at 25 - 400 &micro;g/ml but was not comparable with that of vitamin C. The extract showed good nitric oxide-scavenging activity. IC50 was 474.3 &plusmn; 11.8 &micro;g/ml. It was capable of scavenging hydrogen peroxide in a concentration dependent manner. It showed good activity. Its IC50 was 159.8 &plusmn; 8.2 &micro;g/ml. The IC50 values for ascorbic acid and BHA were 21.4 and 52.0 &micro;g/ml, respectively. The total amount of phenolic compounds in the extract was determined as gallic acid equivalents (22.7 &plusmn; 3.1 mg/g of extract) and total flavonoid contents were calculated as quercetin equivalents (9.6 &plusmn; 1.3 mg/g of extract) from a calibration curve. This plant contained low amount of total flavonoids and phenolic compounds. Its moderate antioxidant activities may be attributed to its low levels of phenols and flavonoids.</p> Antioxidant activity, Helichrysum pseudoplicatum, Radical scavenging, Reducing power 37 43 http://pbr.mazums.ac.ir/browse.php?a_code=A-10-26-5&slc_lang=en&sid=1 Mohammad Ali Ebrahimzadeh 10031947532846001303 10031947532846001303 Yes Pharmaceutical Sciences Research Center, School of Pharmacy, Mazandaran University of Medical Sciences, Sari, Iran. Afsaneh Tavassoli 10031947532846001304 10031947532846001304 No Research Center of Natural Resources of Mazandaran, Sari, Iran.