Present study was undertaken to evaluate the antidiabetic activity of hydroalcoholic extract of powder of rhizome & flower of the plant Alli (Nymphaea nouchali burm.f.) in rats. Diabetes was induced by Single intraperitoneal injection of Streptozotocin monohydrate (STZ)(150mg/kg) and randomly divided in to five groups. Animals were treated with low (200mgkg) & high dose (400mgkg) of hydroalcoholic extract of powder of rhizome & flower of the plant Alli (Nymphea nouchali burm.f.)up to 28 days. Body weight & Blood glucose level (BGL) were measured in weekly basis. After 28 days of treatment animal were sacrificed by mild ether anesthesia blood & vital organ were collected to estimate biochemical parameters & to study histopathological changes. A single-dose administration of Streptozotocin induced hyperglycemia in all the groups. A regular rise in BGL was observed in toxic control groups when compared with the normal control. Daily oral administration of rats with extracts of Alli chooranam (Nymphaea nouchali burm.f.)and standard drug (Glibenclamide, 10 mg/kg), lowered elevated BGL significantly (p < 0.001), and body weight was retrieved in diabetic rats.. The study revealed that Alli chooranam (Nymphea nouchali burm.f.)possesses .promising antidiabetic activity.