OBJECTIVE：To investigate the effects of Alisma orientalis polysaccharides on the insulin resistance and lipid metabolism disorder in type 2 diabetes mellitus （T2DM） rats and its possible mechanism. METHODS： T2DM rat model was induced by high fat diet combined with intraperitoneal injection of streptozotocin （30 mg/kg）. 50 model rats were randomly divided into model group （normal saline）， glibenclamide group （positive control， 25 mg/kg） and A. orientalis polysaccharide high-dose， medium-dose and low-dose groups （400， 200， 100 mg/kg）， with 10 rats in each group. Other 10 normal rats were included in normal control group （normal saline）. All groups were given drugs ig， once a day， for consecutive 6 weeks. After 5 weeks of administration， the glucose tolerance test was conducted. Fasting blood glucose （FBG） levels were measured in rats 0， 30， 60， 90， 120 min after intraperitoneal injection of 2 g/kg Glucose solution， respectively. After 6 weeks of administration， serum levels of FINS and FBG were measured， and HOMA-IR and insulin sensitivity index （ISI） were calculated； serum levels of FFA， LDL-C， HDL-C， TG and TC were detected， and the levels of SOD， GSH-Px and MDA in liver tissue were detected. RESULTS： Compared with normal control group， FBG levels of rats in model group at 0-120 min were increased significantly in glucose tolerance test. After 6 weeks of administration， the serum levels of FINS， LDL-C and ISI， and the levels of SOD and GSH-Px in the liver tissue of the model group were decreased， and the differences were statistically significant （P＜0.05）. Compared with model group， each index of other administration group were improved significantly （P＜0.05）， except that HOMA-IR， the serum levels of LDL-C and HDL-C were not significantly improved in A. orientalis polysaccharide low-dose group （P＞0.05）. CONCLUSIONS： A. orientalis polysaccharide can improve insulin resistance and lipid metabolism disorder in T2DM rats through antioxidant effect.