The infusion of Rosa canina fruit is used in the folk medicine of Iran, Turkey and some other countries for rheumatoid arthritis, influenza, gastrointestinal diseases and also diabetes mellitus. Its hypoglycemic effects have been shown in experimental studies. The objective of this study is to assess the hypoglycemic effects of this herb in type 2 diabetic patients. In this study 60 patients with type 2 diabetes mellitus taking hypoglycemic drugs (except of insulin) with fasting blood glucose (FBG) more than 126 and less than 250 mg/dl, hemoglobin A1C (HbA1c) more than 6, without hepatic, renal and cardiac diseases and not pregnant, allocated in two groups randomly. Patients in group 1 take capsules of powdered aqueous extract of Rosa canina fruit 750 mg BD orally for 3 months. Patients in second group take placebo capsules which filled with corn starch BD orally for 3 months. FBG, 2 hours postprandial blood glucose (PBG) and HbA1c will be measured before and 2 months after interventions and two groups will be compared.