This study was aimed to investigate the protective/preventive and/or curative effects of Silybum marianum seed powder against Methomyl toxication by examining some biochemical parameters and pathological changes hepatic in broiler chicks fed with feeds supplemented with Methomyl and S. marianum seed powder. For this purpose, 4 different groups, each containing 32 animals, were used; Control group (CONT), Methomyl group (MET), S. marianum seed powder group (SMT) and Methomyl+S. marianum seed powder group (MET+SMT). In the study, Methomyl was added to the feeds as 20 ppm and S. marianum seed powder as 10 g‧ kg‒1. The trial period was planned as 28 days, and necropsies of animals from each group were performed daily, and samples were taken for histopathology and biochemistry. In the study, liver enzyme activities and liver tissue oxidative stress markers GPx, MDA and SOD values were found to be similar in the CONT and SMT groups, but statistically higher in the MET group. In the MET+SMT group, the increased parameters were lower than the MET group. The histopathological examinations of liver sections, hyperemia, hemorrhage, hydropic degeneration and fatty changes of hepatocytes, focal necrosis, dissociation of remark cords, mononuclear cell infiltration in the portal area and bile ducts hyperplasia were detected. It has been observed that S. marianum given for preventive/healing purposes reduces histopathological damage and contributes positively in all groups. It has been concluded that S. marianum can be added to poultry diets against Methomyl residues or contamınatıons according to thıs study.