This study investigated antihyperglycemic effects of chronic administration of aqueous leaf extract of Senna fistula in Streptozotocin-induced diabetic rat. Thirty rats were randomly assigned into six groups (A-F). Animals in group A werethe control non-diabetic,in groupB were diabetic and received distilled water, in group C werediabetic,treated with 2.5 mg/kg body weight of Glibenclamide, while animals in groups D, E and F were diabetic treated with 28.57, 57.14 and 114.28 mg/kg body weightrespectively of aqueous leaf extract of Senna fistula for 28 days. At the end of 28 days blood samples were collectedfor the assay ofInsulin, Superoxide Dismutase, Catalase,andGlutathione Peroxidasein serumand liver Glycogen.The result showed that the blood glucose levels of diabetic rats were significantly reduced in the extract and Glibenclamide treated animals when compared with diabetic rats that received distilled water. Similarly, there was a significant increase in serum Insulin level, Superoxide dismutase, Catalase and Glutathione peroxidaseactivitiesand liver glycogenin the extract and Glibenclamide treated diabetic groups when compared with diabetic untreated group. The results indicated that oral administrationof aqueous extract of Senna fistula has antihyperglycemic effect by stimulating Insulin secretion and activating antioxidant enzymes.