Buckwheat has been shown to have various health benefits such as reduction of hypertension and improvement of hypercholesterolemia; however, its effect on diabetes has not been fully elucidated. In this study, buckwheat bran extracts (BBE) inhibited sucrase activity in vitro more effectively than buckwheat. Balb/c mice pretreated with BBE showed dose-dependent reductions of blood glucose, greater than those observed with control mice, within 60 min following oral sucrose administration. Blood glucose levels in mice pretreated with buckwheat extracts were also significantly lower compared to those in control mice within 30 min following oral administration of sucrose. However, rutin, one of the abundant polyphenols of BBE, did not lower blood glucose level. Our data indicate that components of BBE other than rutin have inhibitory activity against sucrase in vivo. These results suggest that BBE could have beneficial effects on diabetes.