Abstract The free-radical degradation and antioxidant activity of polysaccharide from Tremella fuciformis was investigated. In present study, the combination of Fe2+, ascorbic acid and H2O2 was used as degradation regents in order to obtain the lower molecular weight product. The result ascertained oxidative-reduce degradation did not change the main structure of polysaccharides in the test conditions. Five degraded polysaccharides were selected to evaluate their antioxidant activities in vitro. It was found that the degraded sample with lower molecular weight possessed the higher antioxidant activities. It was possible that free-radical degradation is an effective way for enhancing antioxidant activity to decrease molecular weight of polysaccharides.