Abstract: Objective To investigate the effect of different ratios of ω-3/ω-6 polyunsaturated fatty acids (PUFA) on colitis induced by dextran sulfate sodium (DSS) in rats. Methods Forty male SD rats were randomly divided into five groups (n=8). Group A: pure DSS induced colitis with normal diets; group B, group C and group D: diets of ω-3/ω-6 PUFA with the ratio of 1∶1, 1∶3 and 1∶30; Group E: normal controlled group. After six weeks of different diets, colitis were induced by drinking the 3% DSS freely for 7 days, and then drinking water for 12 days in all groups except of group E. The phase above was recycled by twice, and the chronic colitis rats model were established. All the rats were sacrificed when the last cycle was done. Inflammatory severity scoring and histological damage scoring were evaluated. And the level of PGE₂, LTB₄, TNF-α in serum and colon were measured using ELISA. Results The overall inflammatory severity scoring of DSS induced colitis (P＜ 0.05), histological damage scoring (P＜ 0.05) were lowered and the PGE₂ in colon and serum, LTB₄ in colon and TNF-α in serum (P＜ 0.05) were lessened in rats of group ω-3/ω-6 PUFA 1∶1. The imflammation of colitis was improved in some aspects and the LTB₄ in colon and PGE₂ in serum (P＜ 0.05) were decreased in rats of group ω-3/ω-6 PUFA1∶3. The colitis was deteriorated and the inflammatory severity scoring (P＜ 0.05), histological damage scoring (P＜ 0.05) and TNF-α in colon were increased (P＜ 0.05) in rats of group ω-3/ω-6 PUFA 1∶30. Conclusion Diets of high ratio of ω-3 to ω-6 PUFA improves the chronic colitis of rats, and the efficiency of the ratio of 1∶1 is better than 1∶3. However, high ratio of ω-6 PUFA (1∶30) deteriorates the colitis induced by DSS. It suggests that high ratio of ω-3 to ω-6 PUFA can improve the condition of patients with inflammtory bowel disease.