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BACKGROUND The stem bark of Berberis kansuensis Schneid (BK) is a commonly used Tibetan medicine for the treatment of type 2 diabetes (T2D). However, its therapeutic mechanisms remain unclear. AIM OF THE STUDY Our aim is to clarify the role of gut microbiota in the anti-diabetic activity of BK extract. MATERIALS AND METHODS High fat diet combined with low-dose streptozotocin (45 mg/kg) was used to establish a T2D rat model, and the body weight of rats was measured every five days. Fasting blood glucose (FBG), glycosylated serum protein (GSP), insulin resistance index (HOMA-IR), insulin sensitivity index (ISI), lipopolysaccharide (LPS), and three inflammatory factors (TNF-α, IL-1 β and IL-6) were measured to evaluate the anti-diabetic activity of BK. Moreover, pseudo-germ-free animals were prepared by oral administration of an antibiotic mixture (100 mg/kg neomycin, 100 mg/kg ampicillin and 50 mg/kg metronidazole) twice per day for 6 days to assess the role of gut microbiota. Gut microbiota analysis was performed through 16S rRNA high-throughput sequencing method. RESULTS After 30 days of administration, BK extract could significantly decrease the levels of body weight, FBG, GSP, HOMA-IR, LPS, TNF-α, IL-1β and IL-6, and increase ISI levels in T2D rats. However, when the gut microbiota of T2D rats was disturbed by antibiotics, BK could not improve HOMA-IR and ISI levels in T2D rats. The results indicated that the anti-diabetic effect of BK might depend on the gut microbiota. Moreover, sequencing of 16S rRNA genes demonstrated that BK could significantly improve the gut microbiota disorder of T2D rats. Specifically, BK increased the abundance of phyla Bacteroidetes and genera Akkermansia and the ratio of Bacteroides/Firmicutes, while reducing the abundance of phyla Proteobacteria and genera Collinella, [Ruminococcus]_gauvreauii_Group, Escherichia Shigella, Enterococcus, Fusobacterium, Holdemanella, and Prevotella_9 in T2D rats. Additionally, correlation analysis revealed that Akkermansia was positively correlated with ISI, while [Ruminococcus]_gauvreauii_Group, Collinella, Escherichia Shigella, Enterococcus, Fusobacterium, Holdemanella and Prevotella_9 were positively correlated with FBG, GSP, LPS, HOMA-IR, TNF-α, IL-1β, and IL-6. CONCLUSION BK extract has a good anti-diabetic effect on T2D rats. The mechanism by which this extract exerts its action is, at least partly, related to its regulation of gut microbiota.