Background. The plant Cornus mas L. (cornelian cherry) is traditionally used as an antidiabetic supplement; however, there is no related clinical trial. In this study, we evaluated the effects of the fruit extract of this plant on biomarkers of glycemic control in adult patients with type 2 diabetes. Methods. Sixty patients with type 2 diabetes were randomly assigned to two groups to receive either the extract or placebo capsules (2 capsules twice daily) for 6 weeks. Each drug capsule contained 150 mg of anthocyanins. Fasting plasma levels of glucose, insulin, HgbA1C, and triglyceride as well as 2-hour postprandial glucose level (2Hpp) were measured before and after the intervention and finally the mean values were compared between groups. Results. After 6 weeks of intervention, significant increase in insulin level (1.13 ± 1.90 versus −0.643 ± 1.82, P < 0.05) as well as decrease in HgbA1C (−0.24 ± 0.429 versus 0.023 ± 0.225, P < 0.05) and TG (−23.66 ± 55.40 versus 2.83 ± 15.71, P < 0.05) levels was observed in drug group compared to placebo. Conclusion. Daily consumption of the fruit extract of Cornus mas L. improves glycemic control by increasing insulin level and reduces TG serum level in type 2 diabetic adult patients.