Abstract: The antioxidant activities of polysaccharides from three Dendrobium species (Dendrobium officinale, D. wardianum and D. nobile) were investigated in vitro. The results showed that antioxidant ability of Dendrobium polysaccharides correlated well with the increasing of purities and concentrations, and the scavenging activities were the highest at 12 g/L. At this concentration, the scavenging rates by DOPP-I, DWPP-I and DNPP-I were above 75% for DPPH radicals and above 84% for hydroxyl radicals (OH). It was insignificantly different among the three polysaccharides, but they were significantly higher than the control (Vitamin c). The activity of DWPP-I to scavenge superoxide anion radicals (O-2) was significantly higher than DOPP-I and DNPP-I. Thus, antioxidant activity of polysaccharides DWPP-I (from D. wardianum) was higher than those from the other two Dendrobium polysaccharides.