Trichoderma harzianum NBRI-1055 was used, as fungal candidate to enhance the antioxidant activities of soybean matrix by modulating polyphenolic substances during solid-state fermentation. Trichoderma-fermented soybean (TFS) and unfermented soybean (UFS) products were extracted with water (W) and methanol (M). Total phenolic content of TFS-W and TFS-M extracts were significantly higher than that of UFS-W and UFS-M extracts. The effectiveness of extracts for total flavonoid content, antioxidant activity, free radical scavenging activity, reducing power, lipid peroxidation, metal ions-chelation, hydroxyl and superoxide radicals scavenging properties in descending order was TSF-W > TSF-M > USF-M > UFS-W. TFS extracts demonstrated significant protection against oxidative DNA and protein damages caused by hydroxyl radicals. For the specific phenolics profile, HPLC analysis was performed, which showed that the TFS extracts were also higher in isoflavones, flavonoids and phenolic acids, suggesting that this strategy may help to enhance TFS as potential antioxidants for use in preparation of soy food products. (C) 2010 Elsevier Ltd. All rights reserved.