Objective: To investigate the therapeutic effect of duodenal-jejunal bypass (DJB) surgery on type 2 diabetes mellitus (T2DM) in rats and the mechanism. Methods: Rats with T2DM induced by high-fat diet and low-dose streptozotocin injection were randomly divided into DJB group or sham operation group, with 15 rats in each group. The changes in body weight, fasting blood glucose and lipid profiles before and after operation in both groups were examined. At 8 weeks after operation, the specimens of intestinal Roux loop in rats of DJB group and corresponding intestinal segment in rats of sham operation group were harvested and weighed, and then the mRNA and protein expressions of the key enzymes involved in glucose and lipid metabolism were determined by RT-PCR and Western blot analysis. Results: There was no significant difference in fasting blood glucose and lipid levels and body weight between the two groups before operation (all P>0.05). In DJB group compared with sham operation group after operation, the fasting blood glucose level and each lipid index were significantly decreased (all P<0.05), but body weight showed no significant change (2.025 g vs. 0.702 g), the weight of intestinal Roux loop was significantly increased and both mRNA and protein levels of the key enzymes for glucose and lipid metabolism were significantly increased (all P<0.05). Conclusion: DJB can effectively reduce glucose and lipid levels in T2DM rats, and this effect may probably contribute to the alteration in metabolic patterns of the small intestine itself after operation.