In the present work, we have collected 19 species of macroalgae (9 Phaeophta and 10 Rhodophyta) f rom all around of Korea: Dictyopteris divaricata, D. prolifera, Myelophycus cavus, Papenfussiella kuromo, Petalonia zosterifolia, Petrospongium rugosum, Rugulopteryx okamurae, Sargassum fulvellum, S. muticum, Callophyllis japonica, Gloiopeltis tenax, Gracilaria longissima, Gracilaria vermiculophylla, Grateloupia asiatica, Grateloupia lanceolata, Grateloupia sparsa, Grateloupia turuturu, Grateloupia sp, and Polyopes affinis. The macroalgal species were extracted by 70% ethanol (EtOH) for 24 h and evaluated its inhibitory effects on ${alpha}$-glucosidase. Among ethanol extracts, Myelophycus cavus showed the most effectively inhibitory activity ($IC_{50}$, 2.17 ${mu}g/ml$) against ${alpha}$-glucosidase, followed by Sargassum fulvellum (<$IC_{50}$, 8.13 ${mu}g/ml$), Dictyopteris prolifera ($IC_{50}$, 16.66 ${mu}g/ml$), Rugulopteryx okamurae ($IC_{50}$, 50.63 ${mu}g/ml$), and Petrospongium rugosum ($IC_{50}$, 101.62 ${mu}g/ml$). Furthermore, MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assay showed no cytotoxicity on mouse pre-adipocytes cell line (3T3-L1). These results suggest that some edible macroalgae merit further evaluation for clinical usefulness as anti-diabetic functional foods.