Hypoglycemic effect of ethanol extracts of Peganum harmala (commonly known as 'Harmal') seeds has been reported on normal and streptozotocin-induced diabetic rats. In the present study, the authors determine anti-diabetic and anti-oxidative properties of 4-hydroxypipecolic acid (4-HPA) isolated from seeds of P. harmala in C57BL/KsJ-db/db mice. Twelve week old male mice were administered 50 mg/kg body weight (4-HPA suspension were made in 1% gum acacia) for the period of 10 days, and a significant reduction in the fasting blood glucose, plasma triglycerides (TG), cholesterol, free fatty acid, low-density lipoprotein-cholesterol and a significant increase in high-density lipoprotein-cholesterol level was observed with respect to vehicle-treated db/db mice. The anti-oxidant activity of 4-hydroxypipecolic acid was studied in liver and kidney tissues by assessing malondialdehyde levels for lipid peroxidation and enzyme activity of catalase (CAT), glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD). Treatment of 4-HPA significantly lowered the lipid peroxidation in hepatic and renal tissue and increased the activity of CAT, GSH-Px and SOD in treated mice.