Diabetes mellitus is a most serious and chronic disease whose incidence rates are increasing with incidences of obesity and aging of the general population over the world. One therapeutic approach for decreasing postprandial hyperglycemia is to retard absorption of glucose by inhibition of α-glucosidase. Two bromophenols, 2,4,6-tribromophenol and 2,4-dibromophenol, were purified from the red alga Grateloupia elliptica. IC 50 values of 2,4,6-tribromophenol and 2,4-dibromophenol were 60.3 and 110.4μM against Saccharomyces cerevisiae α-glucosidase, and 130.3 and 230.3μM against Bacillus stearothermophilus α-glucosidase, respectively. In addition, both mildly inhibited rat-intestinal sucrase (IC 50 of 4.2 and 3.6mM) and rat-intestinal maltase (IC 50 of 5.0 and 4.8mM). Therefore, bromophenols of G. elliptica have potential as natural nutraceuticals to prevent diabetes mellitus because of their high α-glucosidase inhibitory activity.