The objective of this study was to evaluate the antioxidant activity of cultivated fruiting bodies of an endophytic Xylaria sp. (strain number YX-28), from Ginkgo biloba. The results indicated that the methanol extract exhibited strong antioxidant capacity in both 2,2diphenyl-l-picrylhydrazyl (DPPH) analysis and P-carotene-linoleic acid model system. Total phenolic and flavonoid contents extracted by different solvents were determined using Folin-Ciocalteu procedure and the flavonoid-aluminium method. The results showed that total phenolic and flavonoid contents were the highest in methanol extract (54.51 +/- 1.05 mg gallic acid equivalent/g dry weight and 86.76 +/- 0.58 mg rutin equivalent/g dry weight), while the hexane extract was the lowest (9.71 +/- 0.57 mg GAE/g dw and 10.14 +/- 0.76 mg RE/g dw, respectively). The correlation coefficients from regression analysis showed a positive relationship between total phenolic content in the extracts and DPPH activity (R-2 = 0.7336), as well as between total flavonoid content and DPPH activity (R-2 = 0.9392). Furthermore, GC/MS method was used to confirm the presence of phenolics with antioxidant activity in the methanol extract and resulted in the identification of 41 compounds, esters, phenolics, alkanes, carboxylates and alcohols being the main components. In conclusion, cultivated fruiting bodies of Xylaria sp.YX-28 may have potential as natural antioxidant. (c) 2007 Elsevier Ltd. All rights reserved.