Diabetes is one of the most dreaded noncommunicable diseases affecting mankind. In India, it ranks 4th with a proportional mortality rate of 2%. Pelargonidin, a simplest anthocyanidin, is known to have potential benefit in alleviating experimental diabetes. However, insolubility in water, low stability and rapid biodegradation of pelargonidin and other flavonoids are major constrains of their effective uses. Nanocapsulation is a method of choice to overcome these limitations. We have synthesized pelargonidin-encapsulated nanoparticles by emulsion-diffusion-evaporation method using poly (D, L-lactide-co-glycolide) (PLGA), a bio-compatible polymer. The nanoparticles (P-PLGA) have been characterized by different biophysical techniques. The effects of both free pelargonidin and P-PLGA nanoparticles have been tested in streptozotocin-induced diabetic rat model. Diabetic rats were treated with 0.6 mg pelargonidin/kg body wt. or P-PLGA nanoparticles containing 0.6 mg pelargonidin/kg body wt. by intravenous injection at an interval of 3 days. Administration of two doses of P-PLGA nanoparticles proved efficient in controlling hyperglycemia and hyperlipidemia. Reduced activities of enzymatic antioxidants and elevated oxidative stress markers in diabetic rats were reverted to almost normal levels by P-PLGA nanoparticle treatment. Compared to free pelargonidin, P-PLGA nanoparticles appear to be more effective in controlling the diabetogenic effects of STZ, which may be due to improved dissolution, slow release and long-acting effect of the flavonoid in nanoparticles.