Abstract: Objective To study the morphology and impact of pancreatic fatty infiltration on pancreatic islet in diet-induced obesity rats.Methods Seventy male weanling Sprague-Dawley(SD)rats were randomly divided into two groups:normal chow group(group N)and high-fat diet group(group F).Obesity model covering 34 rats was established successfully after 18 weeks.The obese rats were then divided into three groups according their weight:a mild-obesity group(group A, n=11), a moderate-obesity group(group B, n=11)and a severe-obesity group(group C, n=12).Fasting plasma insulin, free fatty acid(FFA), interleukin 6(IL-6), tumor necrosis factor alpha(TNFα), and pancreatic triglyceride(TG)were determined and pancreatic pathological changes were observed.In addition, insulin resistance index(homeostatic model assessment for insulin resistance, HOMA-IR), insulin β cell function index(HOMA-β), early phase insulin secretion index(ΔI₃₀/ΔG₃₀)and area under curve of insulin(0-120 minutes)were evaluated.Results Compared with group N, pancreatic TG was significantly higher in group C(324.52±55.82 μmol/L vs.269.57±50.45 μmol/L, P<0.05);HOMA-IR was significantly higher in group B(2.27±0.31 vs.1.91±0.26, P<0.01);I30/ΔG30 was significantly lower in group B and C(8.90±2.23 vs.12.56±3.38, P<0.05 and 7.41±2.00 vs.12.56±3.38, P<0.01).The area under the curve of insulin (0-120 minutes)was significantly increased in group B(5867.41±476.27 vs.4976.90±654.93, P<0.01).Conclusion Mild-moderate pancreatic fatty filtration could lead to the delay of insulin secretion in early phase and insulin resistance, while the severe pancreatic fatty filtration could cause the damage of islet β-cells.