Background: Diabetes is a serious chronic disease that can damage the heart, arteries, eyes, kidneys and nerves, leading to death and early disability. Before the discovery of insulin as well as common anti-diabetes drugs, patients with diabetes were treated with medicinal herbs and traditional treatments. One of these effective medicinal herbs is Rhubarb. Rhubarb is prescribed in traditional medicine for various patients, including patients with diabetes. But its effect has not been scientifically reported so far.Purpose: This study was conducted with the aim to determine the effectiveness of Rhubarb stem extract on HbA1C and fasting blood glucose in patients with type II diabetes.Method: In this experimental study, 80 patients with type II diabetes mellitus in Zabol diabetes center, aged 30-60 years old with fasting blood glucose greater than 140 mg/d/ were selected. Patients were randomly assigned into two groups (n = 40) of treatment with capsules of Rhubarb stem and placebo after matching the oral medications. The patients in both groups were studied for fasting blood glucose and HbA1C before and after 1 month of conducting the study.Results: The mean FBS and HbA1C in rhubarb group before the intervention were 288.80 ± 94.49 and 9.62 ± 1.58, respectively, and after the intervention were 226.42 ± 88.89 and 7.83 ± 1.50, respectively. According to the statistical paired f-test and Wilcoxon test a significant reduction was found in FBS and HbA1C with rhubarb intervention (p < 0.05).Conclusion: In diabetes mellitus, as many factors affect the level of blood glucose, they also contribute to reducing blood glucose level and preventing complications. Therefore, considering the positive effects of rhubarb, it can be recommended to use rhubarb extract as an additional treatment to reduce blood glucose level.