Abstract: A polysaccharide coded as ALP1 was prepared and purified from Arctium lappa L. (A. lappa L. ) roots. The hypoglycemic activity of ALP1 was determined both in vitro and in vivo. In vitro hypoglycemic assays, ALP1 significantly inhibited the activity of α-glucosidase, and the IC₅₀ of ALP1 was determined to be 0. 518 4 mg/mL. In vivo hypoglycemic assays, ALP1 significantly reduced fasting blood glucose level, improved glucose tolerance and islet tissue lesions, reduced nitric oxide synthetase activity, decreased reactive oxygen species and malondialdehyde levels, whereas enhancing the activity of superoxide dismutase. The study indicated that ALP1 has good hypoglycemic effect on diabetic mice, and the mechanism may be related to slowing down the absorption of carbohydrates in the intestine by inhibiting the activity of α-glucosidase and reducing the oxidative damage of diabetic mice.