Abstract: The aim of the present study was to elicit the therapeutic effect of Andrographis extract on oxidative stress in aorta as well as liver and kidney of streptozotocin diabetic rats. Aqueous leaf extract of Andrographis paniculata (Andrographis) [400 mg (kg body weight)-1 day-1] was administered to the animals 30 days before diabetes induction and continued for next 6 months after the diabetes induction. There was a significant decrease in the activity of superoxide dismutase (SOD), catalase and glutathione (GSH) in liver and kidney of the diabetic rats. Andrographis administration to diabetic rats resulted in increase in the activity of SOD, catalase and GSH both in liver as well as kidneys. The diabetic rats exhibited endothelial dysfunction as it was evident from the loss of vasodilatory response to the acetyl choline (Ach). This vasodilatory response was restored in the diabetic animals treated with Andrographis. Based on these observations, we conclude that Andrographis reverses the endothelial dysfunction associated with diabetes. This effect appears to be due to its antioxidant properties.