Objective: To investigate the effect of gastric bypass procedure on hepatic lipid metabolism in spontaneous diabetic Goto-Kakizaki (GK) rats and its significance. Methods: Forty male GK rats were equally randomized into experimental group and control group. Rats in experimental group underwent Roux-en-Y gastric bypass operation while rats in control group underwent antroduodenal transaction and then, reanastomosis in situ. The fasting glucose and 2-h oral glucose tolerance test (2-h OGTT) glucose value of the two groups were measured before and 1 week, 2 and 4 weeks after surgery respectively, and the fasting blood levels of free fatty acids (FFA), total cholesterol (Tch) and triglyceride (TG) of rats before and 4 weeks after surgery were also measured. In addition, liver tissues of rats obtained intraoperatively and 4 weeks after surgery were used for immunohistochemical oil red O staining to observe the TG deposits in the liver. Results: Compared with those before surgery, the values of both fasting glucose and 2-h OGTT glucose showed a gradually declining trend after surgery in experimental group, which decreased significantly at 2 and 4 weeks after surgery (all P<0.05); in experimental group, the blood FFA level significantly decreased (P<0.05), while there were no significant changes in the TG and Tch level (both P>0.05), but the TG accumulation in the liver tissue section was markedly reduced. All of the above parameters and measurements in control group showed no obvious changes after surgery compared with preoperative values (all P>0.05). Conclusion: The blood sugar-lowering effect of gastric bypass procedure may be probably associated with its improving hepatic lipid metabolism and decreasing FFA concentration, thereby ameliorating the insulin resistance.