The corrosion inhibition of mild steel in 0.5 M H2SO4 by the Pedalium murex leaves extract has been studied using weight loss methods, potentiodynamic polarization and electrochemical impedance spectroscopy techniques. The results show that the inhibition efficiency increases with the increase of the extract concentration. The adsorption of the extract molecules on the steel surface obeys Langmuir adsorption isotherm and occurs spontaneously. The activation energy as well as other thermodynamic parameters for the inhibition process were calculated. These thermodynamic parameters show strong interaction between inhibitor and mild steel surface.