The aim of the present study was to evaluate the anti-diabetic mechanism of Asparagus officinalis, a dietary agent used for the management of diabetes. Streptozotocin (90 mg/kg) was injected in 2-d-old Wistar rat pups to induce non-obese type 2 diabetes. After confirmation of diabetes on the 13th week, diabetic rats were treated with a methanolic extract of A. officinalis seeds (250 and 500 mg/kg per d) or glibenclamide for 28 d. After the treatment, fasting blood glucose, serum insulin and total antioxidant status were measured. The pancreas was examined by haematoxylin-eosin staining and immunostained β- and α-cells were observed using a fluorescence microscope. Treatment of the diabetic rats with the A. officinalis extract at doses of 250 and 500 mg/kg suppressed the elevated blood glucose in a dose- and time-dependent manner. The 500 mg/kg, but not 250 mg/kg, dose significantly improved serum insulin levels in the diabetic rats. The insulin:glucose ratio was significantly increased at both doses in the A. officinalis-treated rats. Both qualitative and quantitative improvements in β-cell function were found in the islets of the A. officinalis-treated rats. The extract showed potent antioxidant activity in an in vitro assay and also improved the total antioxidant status in vivo. In most cases, the efficacy of A. officinalis (500 mg/kg) was very similar to a standard anti-diabetic drug, glibenclamide. Thus, the present study suggests that A. officinalis extract exerts anti-diabetic effects by improving insulin secretion and β-cell function, as well as the antioxidant status.