Abstract: OBJECTIVE To analyze the difference of bile acid and gut microbiota between type 2 diabetes mellitus(T2DM) patients and normal people, and explore the role of bile acid-gut microbiota axis in T2DM. METHODS The contents of serum bile acid and faecal and gut microbiota in T2DM patients were detected and analyzed by using metabonomics and 16S rRNA sequencing methods respectively. And then the study combined with Spearman correlation analysis, to clarify the metabolic dialogue between bile acid and gut microbiota in T2DM. RESULTS The content of serum bile acid and the abundance of gut microbiota in T2DM patients were different from that in normal people. Compared with normal people, the levels of glycoursodeoxycholic acid, taurochenodeoxycholic acid and glycochenodeoxycholic acid in T2DM patients were significantly lower; the relative abundance of Klebsiella and Plasmodium in T2DM patients was significantly higher and the relative abundance of Parabacteroides, Prevotella,Akkermansia and Bifidobacterium were significantly lower than normal people. Spearman correlation analysis showed that glycoursodeoxycholic acid was positively correlated with the abundance of Parabacteroides and Akkermansia and negatively correlated with the abundance of Klebsiella. CONCLUSION Bile acid-gut microbiota axis is a necessary factor to maintain the body's homeostasis and plays an important role in T2DM.