A total of 45 Japanese and Bangladeshi water fish and fishery products were investigated for radical-scavenging activity using a 1,1-diphenyl-2-picrylhydrazyl- HPLC method. Among the 35 Japanese fish and fishery products (37 items), cutlassfish showed the highest activity (565.7 mg Trolox eq/100 g) and seaweed showed the lowest (24.9 mg Trolox eq/100 g) on a fresh weight basis. Dried bonito, crab (abdomen), Pacific saury, horse mackerel, skipjack, halfbeak, tuna, sand borer, Pacific mackerel, barracuda and anglerfish showed activities of over 100 mg Trolox eq/100 g. The radical-scavenging activities of 10 Bangladeshi fish and fishery products varied from 37.9 to 202.1 mg Trolox eq/100 g. The stronger activity of cutlassfish was attributed to its silver colored skin. The active component was suggested to be uric acid, the metabolic end-product of guanine.