Aqueous extracts of four seaweeds collected from Gulf of Mannar coastal waters were tested for α-amylase and α-glucosidase inhibition properties. The aqueous extracts of seaweeds in the order of Gracilaria edulis, Sargassum polycystum, Ulva lactuca and Gracilaria corticata showed significant inhibitory activity against α-amylase and α-glucosidase enzymes. G. edulis was found to be a potent inhibitor of α-glucosidase with an IC50 value of 46μg/mL. The aqueous extract of S. polycystum at a concentration of 10-100 µg/ml showed maximum α-amylase inhibitory activity with an IC50 value of 60μg/mL. This study warrants further investigation on the antidiabetic activity and identifies the hyperglycemic principle to elucidate their mode of action.