Abstract: The polysaccharide from Ledum palustre L. leaves was obtained by ethanol precipitation, and its content was determined by phenol-sulfuric acid assay. Based on the single-factor test, a orthogonal test was designed to optimize the extracting conditions.The total antioxidant activity and the scavenging effect on DPPH free radical, OH free radical and H₂O₂ by the polysaccharide from L. palustre leaves in vitro were determined by the kit method and chemical method. The antiproliferative activity was evaluated on human liver cancer HepG2 cells in vivo. The results showed that the best extracting conditions of the polysaccharide were:the liquid-solid ratio 30:1(v/w), extraction temperature 80℃ and extraction time 3 h.Under these conditions,the extraction yield of the polysaccharide was 7.86%±0.16% and the purity reached 90.06%. In the range of 1-5 g/L, the antioxidant and antiproliferative activities increased with an increase of mass concentration. At the mass concentration of 5 g/L, the total antioxidant activity was(10.27±0.2) U/mL and reached more than that of 95% Vc with the same mass concentration. The scavenging effects on DPPH free radical and OH free radical in different concentration reached more than those of 90% of Vc with the same mass concentration. The scavenging effect on H₂O₂ reached more than that of 60% Vc with the same mass concentration and the proliferation inhibitory rate of HepG2 cells was 57.41%±0.02% at the mass concentration of 5 g/L.

Key words: Ledum palustre L., polysaccharide, antioxidant, anti tumor