Diabetes mellitus is a chronic metabolic disorder characterized by persistent hyperglycemia, impaired insulin function, oxidative stress, and disturbances in lipid metabolism. The present study was designed to evaluate the anti-diabetic activity of the ethanolic extract of Cleome viscosa in streptozotocin (STZ)-induced diabetic rats. The plant extract was subjected to preliminary phytochemical screening, which revealed the presence of flavonoids, phenolic compounds, alkaloids, tannins, saponins, terpenoids, glycosides, and other bioactive constituents. Diabetes was induced in experimental rats by administration of streptozotocin, and the animals were treated with different doses of ethanolic extract of Cleome viscosa for the experimental period. The anti-diabetic activity was assessed by evaluating body weight changes, fasting blood glucose levels, and oral glucose tolerance test (OGTT). Serum biochemical parameters including total cholesterol (TC), triglycerides (TG), high-density lipoprotein (HDL), low-density lipoprotein (LDL), very-low-density lipoprotein (VLDL), blood urea nitrogen (BUN), and glycated hemoglobin (HbA1c) were estimated. In addition, pancreatic oxidative stress markers such as superoxide dismutase (SOD), catalase (CAT), reduced glutathione (GSH), and malondialdehyde (MDA) were evaluated. STZ administration significantly increased blood glucose levels, impaired glucose tolerance, reduced body weight, altered lipid profile, elevated BUN and HbA1c levels, decreased antioxidant enzyme activities, and increased MDA levels compared with normal control rats. Treatment with the ethanolic extract of Cleome viscosa significantly reversed these alterations in a dose-dependent manner. The higher dose of the extract exhibited marked antihyperglycemic activity, improved lipid metabolism, enhanced antioxidant defense mechanisms, and reduced oxidative damage, with effects comparable to the standard drug metformin.The findings suggest that the ethanolic extract of Cleome viscosa possesses significant anti-diabetic, hypolipidemic, antioxidant, and protective effects against STZ-induced diabetic complications. These activities may be attributed to the synergistic action of its phytoconstituents, particularly flavonoids and phenolic compounds. The present study supports the potential use of Cleome viscosa as a promising natural therapeutic agent for the management of diabetes mellitus and associated metabolic complications.