Nonalcoholic fatty liver disease (NAFLD) is regarded as the most common liver disease with no approved therapeutic drug currently.Silymarin,an extract from the seeds of Silybum marianum,has been used for centuries for the treatment of various liv-er diseases.Although the hepatoprotective effect of silybin against NAFLD is widely accepted,the underlying mechanism and thera-peutic target remain unclear.In this study,NAFLD mice caused by methionine-choline deficient (MCD) diet were orally adminis-trated with silybin to explore the possible mechanism and target.To clarify the contribution of peroxisome proliferator-activated re-ceptor α (PPARα),PPARα antagonist GW6471 was co-administrated with silybin to NAFLD mice.Since silybin was proven as a PPARα partial agonist,the combined effect of silybin with PPARα agonist,fenofibrate,was then evaluated in NAFLD mice.Serum and liver samples were collected to analyze the pharmacological efficacy and expression of PPARα and its targets.As expected,sily-bin significantly protected mice from MCD-induced NAFLD.Furthermore,silybin reduced lipid accumulation via activating PPARα,inducing the expression of liver cytosolic fatty acid-binding protein,carnitine palmitoyltransferase (Cpt)-1a,Cpt-2,medium chain acyl-CoA dehydrogenase and stearoy1-CoA desaturase-1,and suppressing fatty acid synthase and acetyl-CoA carboxylase α.GW6471 abol-ished the effect of silybin on PPARα signal and hepatoprotective effect against NAFLD.Moreover,as a partial agonist for PPARα,silybin impaired the powerful lipid-lowering effect of fenofibrate when used together.Taken together,silybin protected mice against NAFLD via activating PPARα to diminish lipid accumulation and it is not suggested to simultaneously take silybin and classical PPARα agonists for NAFLD therapy.