Corrosion inhibition effect of cymbopogon nardus es sential oil (CNEO) on the mild steel in 1.0 M HCl s olution was investigated by electrochemical (potentiodynamic po larization curves, and electrochemical impedance spectroscopy) and weight loss techniques. The corr osion rate of mild steel was decreased in the prese nce of CNEO. The corrosion inhibition efficiency was found to in crease with CNEO concentration to attain 90% with 1 .50 g/L at 298 K. The polarization studies showed that CNEO ac ts as mixed type inhibitor. The effect of temperatu re on the corrosion rate of mild steel in HCl solution in the absence and presence of CNEO was also studied. Val ues of corrosion inhibition efficiency calculated from wei ght loss technique were in good agreement with thos e obtained from electrochemical techniques. The results showed that the adsorption of the cymbopogon nardus essen tial oil (CNEO) on the mild steel surface obeys Langmuir iso therm. The activation parameters, apparent activati on energy (E a ), the enthalpy of activation ( ∆ H a ) and entropy of activation ( ∆ S a ) for the corrosion of mild steel in 1.0 M HCl in the absence and presence of CNEO were calculated an d discussed.