► Norton grape skin (GSE) inhibits yeast and rat α-glucosidases. ► Norton GSE does not significantly inhibit pancreatic α-amylase. ► Norton GSE reduced postprandial blood glucose in mice. Intestinal α-glucosidases are the key enzymes responsible for starch digestion and absorption and their inhibition has been proven effective in both preventing and treating diabetes through improvement of postprandial hyperglycaemia. This study, for the first time, identified that a Norton grape skin extract (GSE) significantly inhibited mammalian intestinal α-glucosidases but not other digestive enzymes including structurally relevant pancreatic α-amylase. Norton GSE inhibited rat intestinal α-glucosidases through a competitive mode with an IC50 of 0.384mg/ml. Further animal study revealed that the oral intake of Norton GSE (400mg/kg) significantly reduced postprandial blood glucose by 30.9% in the streptozocin-treated male C57BL/6J mice following starch challenge. These findings suggest that Norton GSE may have a unique property of suppressing postprandial blood glucose through a mechanism involving the inhibition of α-glucosidases, thereby providing a novel dietary opportunity for diabetes management.