Introduction: Diabetes Mellitus is a common endocrine-metabolic disease in the world and its incidence has increased over the years, mainly due to poor diet and obesity affecting more than 246 million people worldwide. Objective: The objective of this study was to evaluate the effect of omega-3 on oxidative stress and inflammation in animals with chronic diabetes. Methods: A total of 44 male Wistar rats were used. Induction of diabetes was performed by applying a single dose of streptozotocin (i.p) 70 mg / kg. The animals were divided in six control groups (CO), control treated with omega-3 for 15 days (CO + Ô15D), control treated with omega-3 for 30 days (CO + Ô30D), diabetics (DM) omega-3 for 15 days (DM + Ô15D), diabetics treated with omega-3 for 30 days (DM + Ô30D). Animals received omega-3 at the dose of 4 g / kg body weight or 0.9% NaCl solution per gavage. Treatment started on day 7 after induction of diabetes and animals were euthanized after 15 or 30 days of initiation of omega-3 treatment. Blood and liver were removed and serum glucose, triglycerides, cholesterol, and blood tests were performed. In the liver, the activity of antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), thiobarbituric acid (TBARS) and cytokines IL (interleukin) -1β, IL- 6, IL-10 and TNF-α (tumor necrosis factor) and the immunohistochemical labeling for IL-1β, IL-6 and COX2 (cyclooxygenase-2). Results: Treatment with omega-3 was able to reduce plasma triglycerides and the activity of the antioxidant enzymes superoxide dismutase, catalase and glutathione peroxidase. There was also a significant reduction in the immunohistochemical labeling of IL-1β, IL-6 and COX2, as well as a reduction of TNFα levels without significant alteration in IL-10 in the liver of diabetic animals treated with omega 3. Conclusion: Treatment with ômegsa-3 in diabetic animals reduces triglyceride levels, decreases the activity of antioxidant enzymes and decreases levels of inflammatory cytokines in the liver. These results seem to indicate that omega-3 may be useful as an adjuvant in the treatment of diabetes.