The inhibition of the corrosion of C38 steel in sulfuric acid solution by the essential oil of Eucalyptus globulus (Myrtaceae) has been studied using weight loss, electrochemical impedance spectroscopy and potentiodynamic polarization techniques. Inhibition was found to increase with increasing concentration of the essential oil. The effect of temperature on the corrosion behavior of C38 steel in 0.5M H2SO4 with addition of essential oil was also studied. The adsorption of the essential oil on the C38 steel surface obeyed the Langmuir adsorption isotherm. Values of inhibition efficiency calculated from weight loss, potentiodynamic polarization, and electrochemical impedance spectroscopy are in good agreement. Polarization curves showed that Eucalyptus globulus (Myrtaceae) essential oil behaves as a mixed-type inhibitor in sulfuric acid. The activation energy as well as other thermodynamic parameters for the inhibition process was calculated and discussed. The results obtained showed that the essential oil of Eucalyptus globulus (Myrtaceae) could serve as an effective inhibitor of the corrosion of C38 steel in sulfuric acid solution.