Abstract: The objective of this study was to explore the mechanism and effect of silymarin on hepatocytes lipid accumulation of grass carp (Ctenopharyngodon idellus) induced by oleic acid (OA). Hepatocytes were treated at 400 μmol/L OA with or without silymarin to observe the cell viability by 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and the lipid accumulation by Oil Red O stain. We also tested the effects of silymarin on the antioxidant capacities and the expression of lipid metabolism related gene in hepatocytes in grass carp detected by RT-PCR. The results showed that the cell viability was not affected by the treatment of 400 μmol/L OA with 75—125 μg/mL silymarin in presence for 24h (P>0.05). The intracellular lipid content of hepatocytes decreased significantly after the treatment of 400 μmol/L OA with 100—150 μg/mL silymarin for 24h by Oil Red O stain (P<0.05). Compared with the OA group, SM100 group showed time-dependent trend on the decreasing lipid accumulation (P<0.05). Reduced glutathione (GSH) contents were higher in SM100 group than those in the OA group. The expressions of fatty acid synthase (FAS) and stearoyl-CoA desaturases 1 (SCD1) mRNA were significantly downregulated in SM100 group compared with those in the OA group (P<0.05). These results demonstrated silymarin exerted an inhibitory effect on lipid accumulation by decreasing lipogenesis, and enhanced antioxidative ability in grass carp hepatocytes. Silymarin may shed light on the prevention of fatty liver.