The aim of this study was to investigate the effects of methanolic extract of Diacure a polyherbal formulation for oxidative stress in Streptozotocin induced diabetic rats. Its effect was compared with that of glibenclamide, a reference antidiabetic drug. White albino male rats (Streptozotocin induced) were administered with methanolic extract of Diacure (100mg /kg body wt) orally for 30 days. At the end of 30 days, serum insulin and level, SGOT, SGPT level in serum and liver, catalase, SOD, GPx, GSH and LPO level in serum, liver and kidney were estimated in control, alloxan induced, extract treated and glibenclamide treated rats. Oral administration of methanolic extract of Diacure for 30 days made significant changes in serum, liver and kidney of plant treated rats where compared with untreated diabetic rats. The effects produced by the extract were comparable to that of glibenclamide. In conclusion the methanolic extract of Diacure showed significant antioxidant effect in Streptozotocin induced diabetic rats.