It has been established that hypercholesterolemia is a major risk factor for atherosclerosis. Recent data showed that the incidence of hypercholesterolemia increase in Korea. n-3 Fatty acids lower serum triglyceride profoundly but the effect on serum cholesterol is not clear. This study was performed to assess the effects of low and moderate supplementation of marine n-3 fatty fish on serum cholesterol in young healthy korean woman. Nineteen subjects were divided into two groups. Each group receive an experimental diet supplemented with either 100g (group I) or 200g mackeral(Scomber japonicus) fish(group II) for 1-week. The diet was designed to avoid in which the amount of n-6 fatty acids would be much greater than that of n-3 fatty acids. MUFA, SFA intakes were similar in the two diets. The ratio of n-6/n-3 fatty acids was 1 : 1.l for group I, 1 : 2.51 for group II. The average daily n-3 fatty acids consumption from fish was 3.87g/day (1.03g EPA, 2.84g DHA)for group I, 7.74g/day (2.06g EPA, 5.68g DHA) for group II. Blood samples were obtained 2 times before experimental diet, immediately after experimental diet for 1-week. After experimental diet for 1-week, the serum total-cholesterol levels decreased significantly (16.4$pm$15.1mg/dl, p<0.01) in group II and lowered slightly (13.7$pm$25.8mg/dl)in group I. There were no significant changes from baseline to the end of the study in serum HDL-cholesteol, LDL-cholesterol, HDL-C/T-C ratio, and LDC-C/HDL-C ratio. The results suggest that the moderate levels of marine n-3 fatty fish consumption could improve serum cholesterol in normal subjects, therefore in might be of value in the prevention of atherosclerosis. However the clinical usefulness of moderate n-3 fatty fish consumption of hypercholesterolemic subjects will require further study. Also further studies are required to elucidate the long-term effects of low n-3 fatty fish consumtion.