The inhibitory effect of Athamanta sicula oil was estimated on the corrosion of mild steel in 1M in Hydrochloric acid (HCl) using weight loss, Electrochemical Impedance Spectroscopy (EIS) and Tafel polarization curves. Inhibition was found to increase with increasing concentration of Athamanta sicula oil. The effect of temperature on the corrosion behaviour of mild steel in 1M HCl with addition of Athamanta sicula oil was also studied and thermodynamic parameters were determined and discussed. Values of inhibition efficiency calculated from weight loss, Tafel polarization curves, and EIS are in good agreement. Polarization curves showed that Athamanta sicula oil behave as mixed type inhibitors in Hydrochloric acid 1M. The results obtained showed that oil of Athamanta sicula could serve as an effective inhibitor of the corrosion of mild steel in Hydrochloric acid solution.