In Korea, the concerns about the consumption of soy-based infant formulas have received considerable public attention. In has been known that the n-3/n-6 ratio of soy has a beneficial effect on the health. This study was conducted to investigate whether the soy-based infant formula has an effect on the composition of fatty acids in erythrocytes with regard to the plasma lipid levels in full-term infants. The infants who were delivered at Kyung Hee Medical Center were recruited. Experimental groups were the breast milk group(n=17), soy-based infant formula group(n=12) and casein-based infant formula group(n=19). Anthrophometic and dietary assessments were performed and the composition of RBC fatty acids and blood lipid levels were measured. The body weight, length, chest circumference and head circumference of the subjects were normal growth range showing no significant difference among the experimental groups. The ratio of n-3/n-6 ratio in breast milk, soy-based infant formula and casein-based infant formula were 0.11, 0.14 and 0.13, respectively. N-3/n-6 ratio of the subjects erythrocyte fatty acids for each groups were 0.18, 0.21 and 0.17, respectively. Most of the fatty acids of erythrocyte were not significantly different among the three experimental groups. The blood lipid levels of each experimental group were normal range. The total lipid level of casein-based formula group was higher than that of other experimental groups and LDL-cholesterol level of soy-based formula group was the lowest among the three groups.