Reactive oxygen species (ROS)-related oxidative damages have been implicated in a wide variety of the pathological processes such as atherosclerosis, inflammation and carcinogenesis. A polysaccharide-enriched fraction (PEF) was isolated from Duchesnea chrysantha, a herbaceous plant, and its antioxidant activity was demonstrated using several assay systems in vitro. The PEF effectively inhibited Cu-2+-stimulated low density lipoprotein oxidation in a concentration-dependent way and retarded the conjugated diene formation with the enhancement of the lag phase during oxidation. An assay for DNA strand breaks showed that PEF strongly protected DNA against damage caused by UV or by .OH or .O-2(-) generated in the metal-catalyzed oxidation system. PEF effectively inhibited Nitroblue Tetrazolium reduction mediated by .O-2(-) in a dose-dependent manner. It also competed with 2-deoxy-d-ribose in absorbing .OH generated by gamma-irradiation (600 Gy) and thus inhibited the formation malondialdehyde. In conclusion, these evidences indicate that PEF may act as an antioxidant to scavenge .O-2(-), .OH or LO2. directly. Our findings suggest the possibility that it may play a role as a potential therapeutic antioxidant in treatment of oxidative damage-derived diseases.