A rust converter based on phosphoric acid hadbeen designed and analyzed for the corrosion of mild steel in neutral and acid media. The corrosion inhibition efficiency of the converter was evaluated by means of electrochemical techniques such as electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization in comparison with untreated rusty steel at different temperatures. The forming mechanism of the conversion layer was discussed on account of the formula of the converter preparation together with the X-ray analysis results.