In order to investigate whether Eisenia bicyclis (EB) as a functional food material improves serum lipid status, supplementation of EB powder or EB extract to the high fat/cholesterol diet was tested in 6-week old male Sprague-Dawley rats for four weeks. In the first experiment, four kinds of seaweed powder -Eisenia bicyclis (EB), Undaria pinnatifida (Up), Laminaria japonica (LJ), and Ecklonia stolonifera (ES) were compared with alginic acid (ALG) as well as control. In the second experiment, EB water extract and EB ethanol extract and EB pill containing EB and LJ powder were compared with the EB powder. Amounts of dietary fiber contained in experimental diets were adjusted to provide 5% of diets. Serum total cholesterol was significantly lower only in rats fed LJ or EB powder, but HDL cholesterol was higher in rats fed UP, LJ, ES or EB powder. Ratios of HDL-/total cholesterol of all seaweed groups including ALG were significantly higher than that of the control group. Serum triglyceride was lower in LJ, EB nd ES powder groups than the control group. In comparison of EB extracts, triglyceride level was decreased in rats fed only EB water extract as compared to control rats, but HDL cholesterol was elevated with both water and ethanol extracts. Serum levels of total cholesterol, triglyceride were decreased and HDL cholesterol was increased by the EB pill. Serum levels of thiobarbituric acid-reactive substances were lower in rats fed ES powder, and EB powder, EB water extract or EB pill, as compared to the control rats. Supplementation of EB powder and EB pill reduced serum level of GOT and GPT, respectively, as compared to the control group. In conclusion, EB and EB pill improve serum lipid status and may be utilized as ingredient of functional foods for the purpose of improving serum lipid profile and inhibiting peroxidation of lipids.