Abstract: Objective:To study the preventive effect and mechanism of soybean insoluble dietary fiber(SIDF)on high fat diet(HFD)induced obesity in mice. Methods:Fifty C57BL/6J mice were randomly divided into normal diet control group(ND),high fat diet control group(HFD),and soybean insoluble dietary fiber low(LSIDF),middle(MSIDF)and high dose group(HSIDF). The ND group was fed with normal diet,while the other groups were fed with high fat diet for 20 weeks. After the experiment,the body weight,liver and fat wet mass were counted,liver tissue pathological sections were prepared,serum and liver lipid levels were measured,and real-time fluorescence quantitative polymerase chain reaction was used to determine lipid metabolism-related gene expression levels in mice liver. Results:Compared with the HFD group,the SIDF dose groups could significantly slow down the weight gain of mice,reduce their total cholesterol(TC),triglyceride(TG)levels in serum and liver(P<0.05),and the HSIDF group has better effects than LSIDF,MSIDF group. The liver index(P<0.05)and fat coefficient(P<0.001)of the mice were significantly reduced. The abdominal fat(P<0.001)and periprenal fat weight(P<0.001)of the MSIDF and HSIDF groups were significantly reduced. In addition,the HSIDF group significantly down-regulated the mRNA expression of fatty acid synthase(FAS),diacylglycerol acyltransferase-1(DGAT1),diacylglycerol acyltransferase-2(DGAT2)and stearoyl-CoA desaturase-1(SCD1)(P<0.05). At the same time,up-regulated the mRNA expression of peroxisome proliferator-activated receptor-α(PPARα),carnitine palmitoyl transferase-1a(CPT1a)(P<0.05). Conclusion:IDFS has a preventive effect on HFD-induced obesity in mice,which may be related to reducing lipid synthesis and accelerating fatty acid oxidation,and can be used as a potential dietary supplement.