Abstract: In order to clarify the influence on chemical constituents and antihypoglycemic activity of root of Arctium lappa (AL) after fermented by Aspergillus niger (A. niger), A. niger was applied to conduct fermentation process on AL, and effect of fermentation time on the inhibitory on α-glucosidase and α-amylase as well as on the chemical compositions were revealed. Results showed the inhibitory on α-glucosidase and α-amylase of AL was enhanced after fermentation with increase of 17.8% and 27.9%, respectively. Principle components analysis (PCA) was applied to analyze the chemical components in fermented AL, which clustered into three stages, i.e. first stage (1~5 d), second stage (6~14 d), and third stage (15~20 d). Partial least squares-discriminant analysis (PLS-DA) was applied to find the different components between fermented AL from different stages. The main different components were chlorogenic acid, caffeic acid, and isochlorogenic acid A, etc. The contents of chlorogenic acid, caffeic acid, and isochlorogenic acid A increased after fermentation, which were 2.1, 148.7, and 1.2 folds of unfermented AL, respectively. The increasing of inhibition on α-glucosidase and α-amylase of AL was related with the contents of chlorogenic acid, caffeic acid, and isochlorogenic acid A. Therefore, the content of substances with antihypoglycemic activity in Arctium lappa root could be increased by controlling the fermentation time of Aspergillus niger.