Silymarin was extracted from Silybum marianum (St. Mary's thistle, milk thistle), and has been used to treat liver, spleen and gallbladder disorders due to functions in anti-radical, antioxidant, anti-lipid peroxidation, anti-inflammatory and to protect the stability of plasma membrane. However, it remains unknown whether silymarin has the same functions in juvenile GIFT Oreochromis niloticus. A 9-week feeding experiment was performed to investigate the effects of dietary silymarin levels on growth performance, hepatic lipid metabolism enzymes activities and antioxidant ability in juvenile GIFT[initial body weight (8.17±0.31) g]. Five practical diets were formulated with incorporation of silymarin at the levels of 0 (control), 100, 200, 400 and 800 mg/kg. At the end of the feeding trial, growth performance, body composition, serum biochemical indices, hepatic lipid metabolism enzymes activities and antioxidant enzymes activities were measured. The results were as follows:① Compared with those in the other groups, the highest weight gain rate (WGR), specific growth rate (SGR) and condition factor(CF) were observed in fish fed the diets containing 100 mg/kg silymarin. By contrast, feed conversion rate(FCR) of the fish fed the diets containing 100 mg/kg silymarin was the lowest and significantly decreased compared with control group. Dietary silymarin supplementation significantly decreased hepatosmatic index (HSI) and viscerosomatic index(VSI). There was no significant difference of survival rate among all the groups. ② The lipid content in whole body, muscle and liver was the lowest at the group of 100 mg/kg diet and significantly lower than the control group. Dietary silymarin supplementation significantly decreased triglyceride in serum. The activities of serum aspartate transaminase (AST) and alanine aminotransferase (ALT) were both decreased initially and then increased as silymarin level increased, and the lowest activity of AST and ALT were observed in the group fed 200 and 100 mg/kg diet, respectively. ③ For lipid metabolism enzymes, dietary silymarin supplementation significantly elevated the activities of lipoprotein lipase (LPL) and total lipase (TL) in liver, and the highest activity of lipase (LPS) was in the group of 200 mg/kg diet, while it was significantly lower than the control group. ④ Feed added silymarin significant increased glutathione peroxidase (GSH-PX) activity and decreased catalase (CAT) activity in liver, and significantly reduced malondialdehyde (MDA) content in liver. ⑤ Liver slices of GIFT treated with dietary silymarin addition at 100 mg/kg showed few hepatocytes with empty vacuoles and less nuclear migration. In conclusion, appropriate dietary silymarin supplementation could promote growth performance, decrease muscle, whole body and hepatopancreas lipid contents, and regulate lipid metabolism enzymes and antioxidant ability in liver. On the basis of the above results, the proper dose of silymarin in juvenile GIFT diet was recommended to be 100 mg/kg.