The gum from the seeds of Prosopis pallida (GPP) as an economic and ecological source was used to prepare a new green corrosion inhibitor for P11 steel in an acid medium. The inhibition efficiency of GPP was evaluated using weight loss, open circuit potential, potentiodynamic polarization, polarization resistance, electrochemical frequency modulation, and electrochemical impedance spectroscopy. Considering the five techniques used, an average maximum inhibition efficiency of 80.3% was achieved at 65 ° C using 140 ppm of GPP. It was found that the inhibition efficiency and the adsorption equilibrium constant increased with increasing temperature. The adsorption standard enthalpy was positive and the apparent activation energy decreased with increasing GPP concentration. All these parameters indicate that the adsorption of GPP on the surface of P11 steel occurs through chemical adsorption. Furthermore, GPP acts as a mixed type inhibitor and the results obtained show that it has a high capacity to reduce acid corrosion, particularly at high temperatures.