Technical Abstract: Several plant-based remedies offer cost-effective management of diabetes, but few plant species adapted to North America have been validated for their antidiabetic properties. One such species is serviceberry (Amelanchier alnifolia), found in Browning, MT, which has been traditionally used by the American Indians for managing type 2 diabetes. The objective of this study was to validate and identify potential antidiabetic mechanisms of serviceberry using in vitro and in vivo studies. Serviceberry plant samples consisting of leaves, twigs, and leaves with berries were extracted and fractionated. Ethyl acetate and water fractions were tested for inhibition of alpha-glucosidase activity. In vitro studies demonstrated that leaf extracts of serviceberry are potent inhibitors of mammalian intestinal alpha-glucosidase activity (EC 3.2.1.20). Furthermore, in an animal model of diet-induced obesity and hyperglycemia, serviceberry extracts demonstrated significant inhibition of intestinal alpha-glucosidase activity, and delayed the absorption of carbohydrates, resulting in significant lowering of post-prandial blood glucose concentrations. Thus, the mode of action of serviceberry extracts was similar to that of the antidiabetic drug Acarbose™. These findings validated traditional knowledge and suggest that serviceberry leaf extracts may offer a complementary approach in the treatment and management of diabetes.