The 70% methanol extract from ezoishige (Pelvetia babingtonii de Toni) inhibited the rat-intestinal alpha-glucosidase, sucrase and maltase activities, with IC50 values of 2.24 and 2.84 mg/ml. Sucrose was orally administered with or without the extract to rats at 1000 mg/kg. The postprandial elevation in the blood glucose level at 15 and 30 min after the administration of sucrose with the extract was significantly suppressed when compared with the control. These results suggest that the extract from ezoishige has potent alpha-glucosidase inhibitors and would be effective for suppressing postprandial hyperglycemia.