Flavonoid extracts of fern are conductive to phylogeny and genesiology as well as pharmacological activities. Ferns are widely distributed in Tianmu Mountain. Flavonoid concentrations and antioxidant activity in extracts of 49 ferns from Tianmu Mountain were investigated and analyzed. The result showed that the total flavonoid contents of 49 ferns ranged from 33 to 191.7 mg/g (w/w). Total flavonoid contents and antioxidant activity of fern allies were lower than those of filicinae. Woodwardia japonica(a) contained the highest flavonoid content (191.7 mg/g). The results also showed that most of ferns from Tianmu Mountain had strong antioxidant activity. The extracts from A. rhomboidea showed the highest DPPH center dot scavenging activity, while extracts from W. japonica(a) showed the highest ABTS" scavenging activity. The flavonoid contents of ferns are affected by ecological factors. In general, ferns living under dimmer sunshine have higher flavonoid contents and stronger ABTS(center dot) scavenging activity than those living under strong sunshine. The ferns grown in trees, high altitude and high latitude contain higher flavonoid concentrations, whereas the ferns grown in soil, high altitude contain higher antioxidant activity.