Objective To construct a rat model of nonalcoholic fatty liver disease (NAFLD) by feeding rats fat-rich diet and analyze the effect of insulin resistance (IR)in the development of NAFLD. Methods Male SD rats were randomly divided into normal diet group (NG, n =24) and fat-rich diet group (FG, n =24). At the end of feeding for2 weeks, 4 weeks, 6 weeks or 8weeks, 6 rats in NG and FG were randomly took out. Their weight were recorded, then the serum fasting blood sugar, fasting insulin, triglyceride, total cholesterol, ala-nine aminotransferase and aspartate aminotransferase were measured, and the fasting insulin resistance index and liver index (liver weight (g)/body weight(g) × 100%)was calculated. Then liver tissues were homogenized, and muleic dialdehyde and superoxide dismutase were determined. The hepatic steatosis in all rats was assessed according to the results under light microscope. Results The body weight of rats in NG increased faster than those in FG after six weeks. The liver index of rats in FG was markedly higher than that in NG since the second weekend. The rats in FG began to have hepatocyte steatosis from the second weekend, had insulin resistance, hyperlipidemia, dysfunction of liver and lipid peroxide of liver from the fourth weekend, suffered mild fatty liver from the sixth weekend, and developed to moderate fatty liv-er from the eighth weekend. Conclusions NAFLD with IR model was successfully developed by feeding SD rats with an improved rich-fat diet for 6 weeks. IR may play an important role in the development of NAFLD.