In this study, we investigated the inhibitory effects of Baechu kimchi added Ecklonia cava on the activities of ${alpha}$-glucosidase and ${alpha}$-amylase and its alleviating effect on the postprandial hyperglycemia in STZ-induced diabetic mice. Baechu kimchi added Ecklonia cava (BKE, 15%) was fermented at $5^{circ}C$ for 28 days. Optimum ripened BKE was used in this study as it showedthe strongest inhibitory activities on ${alpha}$-glucosidase and ${alpha}$-amylaseby fermentation time among the BKEs in our previous study. The BKE was extracted with 80% methanol and the extract solution was concentrated, and then used in this study. The BKE extract showed higher inhibitory activities than Baechu kimchi extract against ${alpha}$-glucosidase and ${alpha}$-amylase. The $IC_{50}$ values of the BKE extract against ${alpha}$-glucosidase and ${alpha}$-amylase were 0.58 and 0.35 mg/mL, respectively; BKE exhibited a lower ${alpha}$-glucosidase inhibitory activity but a higher ${alpha}$-amylase inhibitory activity than those of acarbose. The BKE extract alleviated postprandial hyperglycemia caused by starch loading in normal and streptozotocin- induced diabetic mice. Furthermore, the BKE extract significantly lowered the incremental area under the curve in both normal and diabetic mice (P<0.05). These results indicated that the BKE extract may delay carbohydrate digestion and thus glucose absorption.