Widespread use of coccidiostats, in spite of beneficial control of protozoan infections in poultry, implies a risk of residues in edible tissues, and there is increasing interest in the development of strategies for prevention of veterinary drugs residue in food-producing animals. The aim of this study is assigned to clarify the impact of silymarin addendum in the diet on lasalocid concentration in the liver and breast muscles from the broiler. Four groups of chickens received a feed with lasalocid at levels between 75 and 200 mg kg−1. Other four groups received a feed with lasalocid (75–200 mg kg−1) plus silymarin. Significant differences of lasalocid concentrations between the liver and breast muscles were observed. Moreover, the chickens from the groups supplemented with silymarin shown significant decreases of lasalocid concentrations in the analysed tissues. The herbal substance did not counteract the ionophore in the treatment of coccidiosis and did not change biochemical parameters of blood. These findings suggest that silymarin might be used in chicken feeding in order to reduce the risk from lasalocid contamination of the broiler edible tissues.