This experiment was conducted to examine the effects of fish oil supplementation with low does on the lipid concentration and fatty acid composition of plasma and the fatty acid composition of plasma phospholipid and erythrocyte of infants. Among 18 breast-fed infants, 6 were in control group and 12 were in fish oil groups. The subjects in fish oil groups were nursed by their mothers who supplemented with fish oil 1.96g/d or 3.92g/d, respectively for 2 weeks from 10 to 12 weeks postpartum. The nursing mothers consumed their usual diets at home. Blood samples were collected at the final day of experiment. There were no significant changes in daily intakes of total lipid, triglyceride, free fatty acid, phospholipid and cholesterol of infants by fish oil supplementation. However, the content of EPA (eicosapentaenoic acid)increased and that of ARA (arachidonic acid) decreaed significantly in plasma PC(phophatidylchline). And also, there were tendencies to increase triglyceride concentration and to decrease cholesterol and phopholipid concentrations of plasma. As the above results, atherogenic index (AI) showed a tendency to decrease, but not significant. DHA (docosahexaenoic acid) and EPA contents in plasma PC and PE (phosphatidylethanolamin) as well as those of erythrocyte tended to increase. In these results, we concluded that fish oil supplementation with low dose to lactating women does not obviously affect of the plasma lipid concentrations and fatty acid composition of plasma PC and PE as well as erythrocyte. However the increase of EPA content of plasma PC and the tendency to increase DHA and EPA contents of plasma as well as erythrocyte membrane indicate that there may be some beneficial effect on infant lipid metabolism of fish oil intake of nutsing mother were increased.