Medicinal plants are used for their beneficial properties to the health of animals. Recently, it has been found that the use of medicinal plants eliminates industrial pollutants. The objective of our work is to determine and evaluate the effect of two medicinal plants (Thymus algeriensis and Artemisia campestris) on oxidative stress parameters in sheep. The results obtained in liver cells show that medicinal plants have produced a globally antioxidant preventive effect, this is revealed by the significant decrease in the GSH level (199.976±1.913), and the enzymatic activity of CAT (0.699±0.02). In addition, an increase in the enzymatic activities of GST (0.435±0.017), GPx (1.881±0.040) and MDA (29.009±0.086) was observed. These results clearly show an antioxidant effect of medicinal plants on the organism of sheep.