Abstract: Ophiopogon japonicus is a famous traditional medicinal plant，which plays a significant role in improving cellular immune functions. However，the understanding of its action mechanism is not very comprehensive. Firstly，a free radical scavenging assay was applied to analyze its antioxidant capacity in vitro，then H2O2 was used to establish the NIH/3T3 mouse embryonic fibroblasts cell injury model and to further study the intracellular antioxidant effect of Ophiopogon japonicus polysaccharides. Meanwhile，to preliminarily clarify the role of Ophiopogon japonicus polysaccharides in cellular immune function，the activity of α-glucosidase was investigated. The results demonstrated that when the concentration of Ophiopogon japonicus polysaccharides was above 100 μg/mL，its DPPH radical activity was the same as the positive control of ascorbic acid，while the hydroxyl radical scavenging capacity was slightly higher than that of ascorbic acid only when the concentration higher than 20 μg/mL. All these data illustrated the strong antioxidant activity of Ophiopogon japonicus polysaccharides in vitro. In the NIH/3T3 cell injury model induced by H2O2，Ophiopogon japonicus polysaccharides could well reduce the mortality of NIH/ 3T3 cells，the production of singlet oxygen，and the expression of inflammatory factors， which further proved the antioxidant effect of Ophiopogon japonicus polysaccharides. In the α-glucosidase activity assay，the inhibition rate of Ophiopogon japonicus polysaccharides was in a concentration-dependent manner，its inhibition capacity was equivalent to that of acarbose at a concentration higher than 200 μg/mL. These results indicated that Ophiopogon japonicus polysaccharides could be applied as a potential antioxidant therapeutics and hypoglycemic functional food.