The effect of fish oil containing eicosapentaenoic acid （EPA) and docosahexaenoic acid (DHA)on serum lipid, cholesterol and fatty acid compo-sition of juvenile rat was studied. The experimental rats (Spraglue dawley)were divided into three groups with 7 animals each for female and male per group. In the basal diet soybean oil, fish oil and fish oil concentrate were admixed for Group A, Group B and Group C, respectively. After 4 weeks feeding, the contents of serum lipid and cholesterol. in Group B and C were lower than those in Group A (P<0.05).By fatty said assay it showed that the levels of EPA and DHA in the tissues of Group B and C were higher than those in Group A, whereas the contents of arachidonic and docosatetraenoic acid in the tissues of Group A were much higher than those in Group B and C. Interestingly, the analytical results showed that in the rat brain of Group B and C was only DHA well higher in content than that in Group A,and therefore DHA in fish oil would be possible to play an impor-tent role in eugenics. No appreciable difference in body weight gain, weight ratio of viscera to body，total serum protein and alkaline phosphotase among these three groups was observed (P>0.05).