The inhibition behaviour on mild steel (MS) of Robinia pseudoacacia leaves extract (RPLE) in different concentrations in 0.5 M HCl as a green corrosion inhibitor was investigated by using electrochemical techniques, surface analysis. Electrochemical impedance spectroscopy (EIS) measurements demonstrated that RPLE augments the char transfer resistance and then diminishes the double layer capacitance due to the creation of a deterrent layer on the MS with increasing concentration. Polarization measurements have shown that RPLE reducing both anodic and cathodic current density values is a mixed-type inhibitor. Also in with and without RPLE environments, the inhibition efficiencies have decreased with increasing temperature while the activation energy value increases with the addition of RPLE to acidic solution. Thermodynamic parameters (such as and K-ads) were obtained from electrochemical measurements. Adsorption of RPLE components on MS has been descriptived of FT-IR (Fourier Transform Infrared Spectroscopy) and SEM (Scanning Electron Microscopy) data confirming the entity of a obstacle film on MS.