Background: By decreasing oxidative stress and whereby decreasing insulin resistance, it may be possible to decrease complications of Diabetes Mellitus (DM). Green tea and sour tea contain phytochemicals which have anti-oxidative function. The aim of this study is to compare the effect of sour and green tea consumption on insulin resistance and oxidative stress in DM.Methods: This study is a randomized clinical trial in which 100 type 2 diabetes patients were randomly assigned into sour tea group (ST) and green tea group (GT). The patients were instructed to drink 150ml sour tea and green tea infusion, respectively, three times a day for 4 weeks. Fasting blood sugar (FBS), fructosamine, lipid profiles, fasting blood insulin (FBI), homeostasis model assessment of insulin resistance (HOMA-IR); beta cell function (b%), insulin sensitivity (S%) and malondialdehyde (MDA) were monitored.Results: HDL-c significantly increased in both groups. The median of FBI in GT showed significant decrease (8.5 to 6.6 μIU/mL) unlike the ST which showed significant increase (8.2 to 16.3 μIU/mL). The median of HOMA-IR after the intervention in GT showed lower levels than the ST (1.1 vs. 1.6, P=0.004). The median of b% only in ST showed significant increase from 38.2% at the baseline to 47.7% after the intervention. The mean of S% only in ST showed significant decrease after the intervention. Conclusion: This study shows that the use of 150 ml infusion of green tea or sour tea, three times a day for four weeks, has positive effect on insulin resistance and certain lipoproteins in type 2 DM.Trial Registration Number: IRCT201107317161N1