The present study was conducted to investigate the effect of dietary silymarin on milk yield, milk fat, and certain blood parameters of dairy cattle. Silymarin is a naturally accepted hepatoprotectant that is used in the treatment of liver diseases in human beings, and has been tested in dairy cows during peripartum. Animals are subject to subclinical fatty liver. In the first part of the study, the silymarin (20 g/head/day) was supplemented to dairy cattle rations in the last 21 days (peripartum) of pregnancy. In the second part of study, silymarin was added to the rations of Holstein dairy cows for three weeks postpartum. A total of 40 Holstein dairy cows at 2nd lactation with 550-600 kg live weight and average body condition score of 3.5 were used. Dairy cows were randomly separated into two treatment groups (20 cows in each). The first group was control (no addition) and the second group was treatment (silymarin supplemented) group. Treatments significantly increased milk yield, but decreased milk protein. Postpartum bodyweight loss was significantly less in the silymarin group than in the control group. Differences in postprandial plasma triglyceride (TRG) and total cholesterol (TC) levels were found to be significant. Plasma alanine aminotransferase (ALT) and total protein (TP) values of the groups were also significantly different. As a result, it was observed that silymarin supplementation of the ration did not have side effects, and peak milk yields could be achieved earlier with silymarin treatment. Application of silymarin is believed to be useful. It was also observed that silymarin treatments speeded up the metabolic adaptation process of the dairy cows at the beginning of lactation. It was suggested that silymarin should be used in transition periods of dairy cattle.