OBJECTIVE Nutrition disorders caused by a 6.5% maize protein diet (M), unbalanced in its indispensable amino acid pattern, provokes an arrest on cellular proliferation and maturation in the thymus of growing rats. We investigated the effect of diet supplementation with different amounts of omega3 polyunsaturated fatty acid (M = 0 mg/d, M1 = 12 mg/d, M2 = 24 mg/d, respectively) on thymus, plasma lipid concentrations, and hepatic tissue. METHODS A well-nourished age-matched control group received stock diet from weaning. The animals (8 to 10 per group) received the diets for 9 d. At the end of the experimental period, they were killed, thymuses were removed, and cell number, absolute number of T cells labeled by the monoclonal antibody W3/13, plasma lipid profile (total cholesterol, triacylglycerols, high- and low-density lipoprotein cholesterols), and oxidative stress in hepatic tissue were determined. RESULTS Only M2 reached the values of the control group when cell number and absolute number of T cells were compared. No statistical differences were observed among the M, M1, M2, and control group when high- and low-density lipoprotein cholesterols and hepatic lipid peroxidation were considered. CONCLUSIONS The supplementation of a 6.5% maize protein diet with 24 mg/d of omega3 polyunsaturated fatty acid can recover the proliferation and absolute number of T cells labeled with W3/13 without affecting lipid profile and hepatic lipid peroxidation.