Introduction: This study was performed to determine the effects of supplementation of folate on indices of glycemic control, insulin resistance and lipid profile in in men with type 2 diabetes, under metformin (at least 1500mg daily) treatment. Materials and Methods: This was a double-blind randomized controlled clinical trial, in which 68 men with type 2 diabetes participated with written consents. Patients were randomly divided in two groups folic acid 5mg/day and placebo. All the patients received the tablets for 8 weeks. Anthropometric and nutrient intakes data were obtained from each patient, and baseline and 8th week fasting blood glucose, HbA1C, serum insulin, insulin resistance, serum total cholestrol, TG, LDL-C, HDL-C, serum folate and plasma homocysteine were measured. Results: Supplementation with folic acid led to 6.3 percent decrease in HbA1C (P=0.019), 9.5 percent decrease in fasting blood glucose (P=0.006), 15.1 percent decrease in serum insulin (P=0.028), 17.2 percent decrease in insulin resistance (P=0.043) and 20 percent decrease in plasma homocysteine (P<0.001), 18.4 percent increase in serum folate (P<0.001). No significant changes occurred in the placebo group (P>0.05).  Conclusion: A pharmacological dose of folic acid supplementation decreased plasma level of homocysteine and improved glycemic control, insulin resistance and folate levels, a finding which sugqests a safe and inexpensive therapy for lowering homocysteine and improving the overall management of diabetic patients.