A randomized, double-blind, placebo-controlled study of fermented sea tangle (FST) was conducted using 48 healthy volunteers with high levels of γ-glutamyltransferase (GGT).Participants (n=48) were divided into a placebo group and a FST group, which consumed FST (1.5 g/day) for 4 wk.Serum GGT, aspartate aminotransferase (AST), alanine aminotransferase (ALT), and lactate dehydrogenase (LDH) levels were determinedPlasma 8-isoprostane, 8-hydroxydeoxyguanosine (8-OHdG), and protein carbonyl contents, which indicate lipid peroxidation, DNA damage, and oxidation of protein, were determinedDecreased serum GGT was found in FST consumption group, compared to the placebo group [mean values (IU/L): 78.71±19.14 and 116.75±38.55, resp., p<0.001].Administration of FST significantly (p<0.05) decreased levels of serum AST [mean values (IU/L): 31.08±7.25 and 26.79±6.53 resp., p<0.001] and ALT [mean values (IU/L): 42.63±18.99 and 31.83±14.21, resp., p=0.001], compared to the placebo group, and significantly (p<0.05) decreased concentrations of plasma 8-isoprostane, 8-OHdG, and protein carbonyl levels.