Ethanolic extracts of fruit bodies of 5 species (8 strains) of the genus Phellinus, and isolated fractions derived from 1 of these extracts (Ph. baumii PB-10), were evaluated for antioxidant activity, inhibitory effects on the growth of human tumor cells, and the capacity to protect PC12 cells against H2O2-induced oxidative damage. Extracts of all 8 strains of Phellinus spp. exhibited antioxidant activity and protected PC12 cells against oxidative damage at different magnitudes of potency. The strongest antioxidant activity was exhibited by extracts of Ph. baumii PB-10, with recorded IC50 values for superoxide radical and hydrogen peroxide scavenging activity of 3.76 microg/mL and 4.24 microg/mL, respectively. Radical-scavenging activity and protection levels against H2O2-induced damage to PC12 cells were highly correlated with the flavonoid content of the extracts and isolated fractions. All the extracts inhibited L1210, SW620, and MCF-7 tumor cell proliferation at 200 microg/mL concentrations, but inhibition was not correlated with the flavone content of the test samples and was clearly dependent upon the presence of other, as yet, unidentified components. Our data indicate that fruit bodies of species of the genus Phellinus represent a potentially valuable source of natural antioxidants of relevance to both the health and food industries.