The present work focuses on evaluation of the toxic effects of an exposure to lead (Pb) on the liver mitochondria function in Wistar rats and the protective role of the fennel essential oils (FEO). The experiments were conducted on Wistar rats, which were treated daily through orally gavages during 21 days. 24 animals were divided into four groups of 6 rats each one: the control group received water, while group II received FEO (0.5 mg/kg); group III received Pb (25 mg/kg), and group IV received Pb + FEO in the doses of (0,5 + 25 mg/kg). The mitochondrial dysfunction induced by lead is expressed by reducing mitochondrial respiration (O2 consumption) associated with an increase in mitochondrial swelling and permeability compared to the control group. A disturbance in the rates of oxidative stress biomarkers was also observed. This disturbance was expressed by an increase of the MDA rate and the Cytochromes C activity associated with depletion in the GSH rate and GPx activity compared to the control group. The rat’s co-treatment with FEO restored all these parameters to values similar to the Control. The whole of these results shows well that the exposure to the lead causes disturbances on the level mitochondrion, which are attenuated by fennel essential oils.