Introduction: Syndrome X or metabolic syndrome is a collection of risk factors which can lead to diabetes and cardiovascular diseases and result in death. Considering the important role of oxidative stress in causing the complications of this syndrome, the aim of this study was to investigate the effect of vitamin E supplementation on insulin resistance and associated risk factors in patients with metabolic syndrome. Materials and Methods: A randomized double blind placebo controlled clinical trial with parallel design was conducted on 70 metabolic syndrome patients, 29-57 years old, who were randomly divided into two groups one using 400 mg vitamin E (n=35), and group 2- given placebos (n=35) for 3 months 24 hour dietary recalls were completed in the beginning, and end of first, second and third months for each patient. Serum glucose and lipoprotein by enzymatic, Insulin by RIA, uric acid and CRP by colorimetric, insulin resistance by HOMA-IR methods were measured. For statistical analyses, student’s t-test, paired t-test, chi square and ANOVA were used. Results: There was significant difference in systolic and also diastolic blood pressure at the end of study in the vitamin E group compared to initial values (p=0.00, p=0.09 respectively). In this group, systolic blood pressure, serum glucose and triglycerides (TG) had significant decrease at the end of the study compared to the control (p= 0.003, p= 0.02, p= 0.04 respectively). Serum glucose, TG, insulin and insulin resistance had significant differences in the vitamin E group at the end of study compared to the beginning (p=0.03, p=0.01, p=0.03, p=0.04) Serum TG, glucose and insulin were 221.08±59.54, 114.07±9.64, and 8.3±1.6 at the beginning and 197.65±56.77, 101.05±9.7 and 7.48±1.55, respectively at the end of study. Conclusion: In metabolic syndrome patients, 400 mg vitamin E for 3 months had benetical effects on blood pressure, TG, glucose, insulin and insulin resistance.