Six diets containing graded levels (0.79，0.83，0.85，0.88，0.92 and 0.94%) of n-3 highly unsaturated fatty acids (n-3 HUFA) with a constant DHA/EPA, were fed randomly to six groups (Diet 1-6) of fish with triplicate ［average weight, (8.08±0.09) g; 20 fish/replicate］ to determine the effects of dietary n-3 HUFA on growth and lipid metabolism in juvenile black sea bream (Sparus macrocephalus). Results of the 8week growth trial showed that: (1) Hepotasomatic index (HSI) and intraperitoneal fat (IPF) ratio of juvenile black sea bream decreased with the increase of dietary n-3 HUFA and the values in Diet 5 and 6 were significantly lower than those in other four groups (P<0.05). Adipocyte diameter in IPF was decreased by dietary n-3 HUFA and the significance occurred between Diet 3 and 6. Lipid content in muscle was significantly affected by dietary n-3 HUFA and reached the bottom in Diet 4. No significance was found in whole body proximate composition of juvenile black sea bream. Concerning the fatty acid composition, ∑SFA and the main constituent,C16:0 were negatively correlated with dietary n-3 HUFA, while ∑n-3 HUFA content was obviously increased among all the treatments. DHA to EPA ratios (DHA/EPA) in liver, dorsal muscle and IPF were unchanged with the supplementation of dietary n-3 HUFA. Quadratic analysis based on weight gain rate (WGR) indicated that dietary n-3 HUFA requirement for black sea bream was 0.87% DM. (2) Determination of fatty acid synthase (FAS) and hormonesensitive lipase (HSL) activities showed that FAS activity kept constant in Diet 1 to 4, and then decreased significantly with further increment of dietary n-3 HUFA. HSL activity in IPF increased significantly with the elevation of dietary n-3 HUFA level and increased to almost two times in Diet 6 (0.94%n-3 HUFA). Gene expression of FAS changed following the similar trend with FAS activity in liver; while expression of HSL in IPF was positively correlated with dietary n-3 HUFA level. In summary, we can deduce that n-3 HUFA regulation in lipid metabolism was realized by affecting the lipogenesis and lipolysis at the same time.