ABSTRACT: Diabetes mellitus (DM), one of the most devastating illnesses, has a major influence on one's health and quality of life. Phytotherapy has a good prospect in the treatment of diabetes since it is less toxic and has fewer adverse effects than synthetic medications. In Asian, Oriental, and Latin American nations, Rauvolfia tetraphylla L. (RT) is extensively used in traditional ethnomedicine. In the current study, in vivo anti-diabetic activity of RT leaf extract was evaluated following standard procedures. Intraperitoneal injection of 90 mg/kgbwt of alloxan monohydrate was used to induce hyperglycemia. The experiment was conducted with six groups of male Wister rats (120.20±15.25 g) and administered 50, 100 and 150 mg/kgbwt of the RT extract, standard drug-glibenclamide (6 mg/kgbwt) treated group, normal sterile saline treated group and one non-diabetic untreated group, respectively. After 21 days, rats receiving 150 mg/kgbwt of the fraction had blood glucose levels of 109.002.33 mg/dL as compared to 78.911.90 mg/dL for the group receiving glibenclamide. Triglycerides, total cholesterol and LDL cholesterol levels were decreased while HDL cholesterol levels were raised as a result of the RT extract treatment. There was a significant increase (p<0.05) at 150 mg/kgbwt in the levels of catalase (34.36±0.30 U/mL), superoxide dismutase (70.66±0.56 U/mL) and reduced glutathione (100.64±3.25 μg/mL) activities compared with 24.86±0.76 U/mL, 33.32±0.73 U/mL and 63.82±2.10 μg/mL respectively for the control groups. The administration of diabetic rats with plant extracts over a 21 days period returned blood glucose levels close to normal control group (89±0.88 mg/dL). For all the parameters evaluated, the results were observed significant and in close comparison with the standard antidiabetic drug, glibenclamide. Along with all other anti-diabetic parameters, the pathological morphology of the kidney, liver, and pancreas is normalized. This indicates that the extracts of RT have diminishing effect on severity of diabetes.