Propolis, an extremely complex resinous material, exhibits valuable pharmacological and biological properties attributed to the presence of polyphenols. In this study, we determined the antioxidant properties of lyophilized aqueous extract of propolis (LAEP) from Erzurum province of Turkey and correlated the values with total levels of polyphenolic compounds. In order to estimate the capacity of LAEP to act as antioxidants, we studied its 1,1-diphenyl-2-picryl-hydrazyl radicals (DPPH center dot), 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) radicals (ABTS(center dot+)), N,N-dimethyl-p-phenylenediamine radicals (DMPD center dot+), superoxide anion radicals (O-2(center dot-)) and hydrogen peroxide (H2O2) scavenging activity, total antioxidant activity, ferric ions (Fe3+) and cupric ions (Cu2+) reducing ability, ferrous ions (Fe2+) chelating activity. LAEP inhibited 93.2% lipid peroxidation of a linoleic acid emulsion at 30 mu g/mL concentration. On the other hand, BHA, BHT, alpha-tocopherol and trolox displayed 83.3%, 82.1%, 68.1% and 81.3% inhibition of peroxidation at the same concentration, respectively. Quantitative amounts of caffeic acid, ferulic acid, syringic acid, ellagic acid, quercetin, alpha-tocopherol, pyrogallol, p-hydroxybenzoic acid, vanillin, p-coumaric acid, gallic acid and ascorbic acid were detected by high performance liquid chromatography and tandem mass spectrometry (LC-MS/MS). This study will bring an innovation for further studies with regard to the antioxidant properties of LAEP. (C) 2010 Elsevier Ltd. All rights reserved.