Forestry biomass, generated as result of forest operations and cleaning of the Galician (NW Spain) mountains, was studied as a potential source of natural antioxidants. The main goals of present work were to determine the optimal conditions for the extraction of antioxidant compounds from the forestry biomass using aqueous solutions of methanol and to investigate the antioxidant capacity of extracts obtained. At first, several preliminary extraction experiments were conducted to study the kinetics of extraction process under selected conditions (50% aqueous solution of methanol at 25, 50 or 75 degrees C). The experimental results were fitted to Peleg's, Elovich's and Page's kinetic models. The Peleg's model was proved to be the best to describe the kinetics of extraction process. In a second stage experiments were planned according to an incomplete 33 factorial experimental design to analyse the influence of operational conditions on total phenols content and FRAP (Ferric Reducing Antioxidant Power), ABTS (2,2'-azino-di(3-ethylbenzothiazoline-6-sulfonic acid)) and DPPH (2,2-diphenyl-1-picrylhydrazyl) antioxidant capacity of extracts. The examined conditions were as follows: temperature (25-50-75 degrees C), time (5-55 105 mm) and methanol concentration (10-50-90%). The highest temperature assayed (75 degrees C), a moderate solvent concentration (50%) and an extraction time of 55 mm were selected as the optimum extraction conditions using the response surface methodology. The following compounds were identified in the extract obtained under optimum conditions: monogalloyl glucose, digalloyl glucose, (-)-gallic acid, (-)-epicatechin, (+)-catechin, ellagic acid and quercetin 3-O-rhamnoside. (C) 2012 Elsevier Ltd. All rights reserved.