The total superoxide dismutase (T-SOD), catalase (CAT) and malondialdehyde (MDA) in serum were measured to evaluate the effect of different supplemental levels of unsaturated fatty acid on lipid peroxidation in Monopterus albus. Through the L9(33) orthogonal design, the experimental diets were added with different levels of safflower seed oil (source of C18∶2n-6), linseed oil (source of C18∶3n-3) and EPA/DHA mixture oil (source of C20∶5n-3+C22∶6n-3) on a basal diet. One thousand Monopterus albus with average body length of (34.5±2.4) cm and average body weight of (37.8±3.5) g were randomly divided into control group and 9 experimental groups, and each group contained 2 replicates and each replicate contained 50 Monopterus albus. Control group fed with basal diet, and each experimental group fed with 1 experimental diet. The experiment lasted for 31 days. The results were showed that, no significant difference was found in serum T-SOD activity among all groups (P>0.05). The serum CAT capacity in experimental groups was lower than that in control group, but no significant difference was found (P>0.05). The serum MDA content in groups 1, 3, 4, 5, 6, 7 and 8 was significant lower than that in control group (P<0.05). Combination with the growth experiment, the metabolism of free radicals and lipid peroxidation kept higher growth performance and the best state of equilibrium when the content of C18∶2n-6, C18∶3n-3 and C20∶5n-3+C22∶6n-3 were 1.30%, 1.55% and 0.25% in diet, respectively.［Chinese Journal of Animal Nutrition, 2009，21(6):1018-1022］