Abstract: Objective To observe the influence of n-3 polyunsaturated fatty acids(n-3PUFAs) on colorectal cancer of SD rats. Methods A total of 60 SD colorectal cancer rats were randomly divided into two groups, experimental group treated with intragastric administration of n-3PUFAs, and control group treated with the same amount of normal saline. Both groups were given MNU enema. During the experiment, general condition of the rats was observed. After 16 weeks, we dissected the rats and observed the tumors. Tumor pathology was determined by HE sections. The n-3PUFAs concentration of erythrocyte membrane was measured by gas chromatography method in two groups. Results Compared with control group, general condition change was lighter (P<0.01 or 0.05), n-3PUFAs concentration of red blood cell was higher(P<0.01) and incidence of cancer was lower (P<0.05) in experimental group. Conclusion n-3PUFAs could improve general condition and prevent occurrence of colorectal cancer in SD rats.