Background: Pomegranate seed oil and its main constituent, punicic acid, have been shown to decrease plasma glucose and have antioxidant activity. The objective of the present study was to examine the effects of pomegranate seed oil on rats with type 2 diabetes mellitus. Method: Six groups (n=8 each) of male Sprague-Dawley rats, comprising a control, a diabetic (induced by Streptozocin and Nicotinamide) receiving water as vehicle, a diabetic receiving pomegranate seed oil (200 mg/kg/day), a diabetic receiving pomegranate seed oil (600 mg/kg/day), a diabetic receiving soybean oil (200 mg/kg/day), and a diabetic receiving soybean oil (600 mg/kg/day), were used. After 28 days of receiving vehicle or oils, blood glucose, serum levels of insulin, malondialdehyde, glutathione peroxidase, and lipid profile were determined. Results: The diabetic rats had significantly higher levels of blood glucose, serum triglyceride, low-density lipoprotein cholesterol, total cholesterol, and malondialdehyde and lower levels of serum insulin and glutathione peroxidase. Rats treated with pomegranate seed oil had significantly higher levels of serum insulin and glutathione peroxidase activity, and there were no statistically significant differences in terms of blood glucose between them and the diabetic control group. Conclusion: The findings of the present study suggest that pomegranate seed oil improved insulin secretion without changing fasting blood glucose.