OBJECTIVE： To study the antioxidant activity in vitro of neutral polysaccharides and its graded component from 3 samples of white ginseng and red ginseng. METHODS： The decoction method was used to extract the crude polysaccharides from white ginseng， 100 ℃ and 120 ℃ processed red ginseng； the crude polysaccharides were further separated through ion exchange column to extract neutral polysaccharides； Sephadex G-75 gels filter column was used to grade the neutral polysaccharides according to the molecular weight， antioxidant activity in vitro of 9 samples in 3 neutral polysaccharides and were detected by DPPH and OH free radical scavenging test and reduction capacity test （FRAP value）， and vitamin C was used as positive control. RESULTS： The 3 neutral polysaccharides all obtained component Ⅰ and component Ⅱ after grading. Neutral polysaccharides and its graded component showed certain antioxidant activity in vitro in a certain concentration range， and increased by concentration increasing. The activity of neutral polysaccharides and component Ⅱ from 120 ℃ processed red ginseng was the strongest， of which 50％ inhibitory concentration （IC50） on DPPH free radical was 0.258 g/L and 0.253 g/L， on OH free radical was 7.157  g/L and 6.845      g/L， FRAP values were 2.8 and 3.0 mmol/L （when concentration was 1.2 g/L）， respectively. CONCLUSIONS： The antioxidant activity in vitro from 120 ℃ processed red ginseng is higher than that of 100 ℃ processed red ginseng and white ginseng， in which component Ⅱ makes important contribution to the antioxidant activity.