Abstract INTRODUCTION: Diabetes is regarded as serious condition for both the individual and the society. Its rapidly increasing global prevalence is a significant cause for concern. One of the most important reasons of mortality in diabetic patients is atherosclerosis. Many epidemiologic studies have shown that the total homocysteine concentration is a risk indicator for cardiovascular disease. Studies have shown that its concentration is increased considerably in diabetes mellitus. Epidemiological data indicate that the consumption of omega-3 unsaturated fatty acids (n-3FA) leads to a reduction in cardiovascular disorders and may protect against metabolic diseases. In recent years, many have studied omega-3 fatty acids but still, it cannot be used as an additive. This study aimed to evaluate the effects of ω3 on homocysteine in type 2 diabetic patients. METHODS: A randomized double blind placebo controlled clinical trial was conducted on 80 type 2 diabetic patients aged 45-85 years with diabetes for at least 2 years. Anthropometric indices including body mass index (BMI) and medical history were obtained. Diabetic patients were randomly assigned to either the case or the control group. Each subject received 3 capsules per day (omega-3 or placebo) for a period of 2 months. A sample of 10 ml blood was collected from each subject at the beginning and at the end of the study. Serum homocysteine was measured by Hitachi autoanalyzer with the Enzymatic Cycling method. Nutrient intake was estimated using 24-hour dietary recall questionnaire at the beginning and at the end of the trial for 2 days and analyzed by FPII. T-test was also used to compare the groups. RESULTS: Comparison of mean ± SD (standard deviation) of BMI and food intake did not show any difference between the case and control groups. homocysteine levels were 3.10 µmol/lit and 0.126 µmol/lit in the case and control groups, respectively, and the difference was significant. CONCLUSION: Omega-3 fatty acids supplementation (3 g/per day) in the form of capsules can decrease homocysteine content in diabetic patients. Keywords: Type 2 diabetes mellitus, omega-3 fatty acid, homocysteine.