Abstract: Objective To explore the effect of different ratios of n-6 and n-3 polyunsaturated fatty acids(PUFA) combined with food restriction on ulcerative colitis induced by dextran sulfate sodium(DSS) in rats.Methods Forty-eight female rats were randomly divided into six groups:control group,model control group,5:1 regular group(PUFA n-6/n-3=5:1),three calories restriction groups(PUFA appended:none,n-6/n-3=5:1,n-6/n-3=10:1;with energy restriction of 60%).All rats were fed with specific diet for 14 weeks.Then the rats in ulcerative colitis model groups were given 5.0% DSS in drinking water for 7 days.Body weight,bloody stools and diarrhea were recorded during the experiment.All rats were sacrificed using an overdose of anesthesia 3 days after the establishment of the model.The colon samples were extracted,and the colon weight/length ratio(mg/cm),overall score and histological score were assessed.The activities of myeloperoxidase(MPO),superoxide dismutase(SOD),glutathione peroxidase(GSH-Px),and content of malondialdehyde(MDA) in serum were detected with biochemistry methods.Results Compared with DSS model control group,the disease activity index(1.14±0.74) in the PUFA n-6/n-3=5:1 and calories restriction group was not significantly different(P>0.05);the weight/length ratio(71.09±4.59 mg/cm) in the PUFA n-6/n-3=5:1 and calories restriction group was significantly lower(P<0.05);the overall score(1.57±1.27) in the PUFA n-6/n-3=5:1 and calories restriction group was significantly lower(P<0.05);the histopathological score(1.14±0.26) in the PUFA n-6/n-3=5:1 and calories restriction group was significantly lower(P<0.05);the activity of SOD(207.92±21.54) and GSH-Px(393.87±81.60) in serum in the PUFA n-6/n-3=5:1 and calories restriction group were significantly higher(P<0.05);the content of MPO(157.61±12.56) and MDA(4.91±0.67) in the PUFA n-6/n-3=5:1 and calories restriction group were significantly lower(P<0.05).Conclusion The effects of food restriction and PUFA n-6/n-3=5:1 in protection of DSS-induced ulcerative colitis are significant and the mechanism may be related to antioxidation.