In this study,the polyphenols in blueberry leaves were extracted by ultrasonic method,and the total phenolic contents in the extracts before and after purification were determined.By using the liquid chromatography-mass spectrometry (LC-MS),the phenolic composition was first identified.Then,the stabilities of polyphenols during treatments at different temperatures and pH values were investigated.The in vitro hypoglycemic activity of the purified polyphenols was evaluated based on their inhibitory effects on α-amylase and α-glucosidase,where the acarbose was used as the positive control.As to determine the type of inhibitory effects of blueberry leaf polyphenols against the hypoglycemic-related enzymes,the enzymatic kinetics and Lineweaver-Burk double reciprocal method were used.The results showed that the total phenol content increased by 41.19%,and the α-amylase and α-glucosidase inhibitory activities of polyphenols increased by 138.70% and 12.42%,respectively,compared with those before purification.The blueberry leaf polyphenols were proved to be stable at low temperature (30-50 ℃) and acidic environment (pH 2.0-8.0 and 3.0-5.0),possessing the high α-amylase and α-glucosidase inhibitory activities (IC₅₀ of 10.926 and 7.276 μg/mL,respectively) in a mixed-reversible manner.These above results indicated that the purified polyphenol extracts obtained from blueberry leaves had great in vitro hypoglycemic activities and provides the theoretical basis for the research and development of blueberry resources.