Abstract: Objective To study the effects of different ratios of n-3/n-6 polyunsaturated fatty acids(PUFA)in feed on lipid metabo lism of SD rats.Methods According to their total serum cholesterol level,58 male Sprague-Dawley rats were randomly divided into 6 groups,and were supplied with common diet,high fat diet,high fat diet with n-3/n-6 PUFA of 1:1,high fat diet with n-3/n-6 PUFA of 1:5,common diet with n-3/n-6 PUFA of 1:1,and common diet with n-3/n-6 PUFA of 1:5,respectively.We collected blood samples at 15,30,45 days and measured the lipid level in the plasma.After 45 days,the rats were sacrificed,and adipose tissues(subcutaneous,mesenteric,retroperitoneal,epididymal)were removed and weighed.Also,we measured the expression of peroxisome proliferator-activated receptor γ(PPARγ)and AMPK-α2 in the liver.Results Four diets with different ratios of n-3/n-6 PUFA resulted in significant lower contents of triglycerides(1.15 ±0.37,1.25±0.56,1.00±0.25,1.17±0.30 vs 1.73±0.33 mmol/L),total cholesterol(1.80±0.18,1.89±0.20,1.41 ±0.21,1.58±0.16 vs 2.23±0.19 mmol/L)and LDL cholesterol(1.00±0.23,1.25±0.18,1.06±0.13,1.25±0.14 vs 1.53±0.27 mmol/L)in the plasma compared with the high fat diet group(P<0.05).The PPARγand AMPK-α2 mRNA level in the liver increased significantly in the four PUFA diets compared with that of the high fat group(P<0.05).Conclusion These results indicate that dietary PUFA can improve lipid metabolism and decrease fats accumulation,which may be related with the increased expression of fatty acid oxidation gene PPA Rγand AMPK.