INTRODUCTION: Pomegranate is known as a functional food which has multiple health-promoting activities. It has been assessed for patients with metabolic syndrome. Specifically, an antidiabetic activity of its juice and plausible mechanisms for its action have been shown in multitudinous studies. The aim of this study was assessing the effects of complementary treatment with pomegranate seed powder (PSP) oral supplementation on patients with type 2 diabetes mellitus (T2DM). METHODS: Sixty patients were treated for 8 weeks by 5 g PSP or placebo, twice daily. Fasting blood glucose (FBG), glycated hemoglobin (HbA1c), total cholesterol, and triglyceride (TG) were recorded as the outcome measures at the beginning and after the intervention. The findings were analyzed using the independent t test and Mann-Whitney U test. RESULTS: After 8 weeks, the mean differences of FBG, HbA1c, cholesterol, and TG were significantly decreased in the PSP group when compared with the placebo group (p value <0.05). In addition, post-intervention values of FBG and HbA1c were significantly lower in patients treated with PSP compared to the placebo group (p values = 0.02 and 0.01, respectively). However, the latter comparison regarding cholesterol and TG showed no significant differences (p values = 0.51 and 0.26, respectively). CONCLUSION: It seems that complementary treatment with PSP may have beneficial effects on FBG and HbA1c of patients with T2DM. However, its effect on TG and cholesterol was equivocal.