Adsorption  isotherm  of  N,N′-bis(2,4,6-trihydroxyacetophenone)-2,2-dimethylpropandiimine  (THAPDP)  as  an  environmentally  friendly  Salen  Ligand corrosion inhibitor on mild steel was studied in alkaline solution (pH=10) containing 3% NaCl. Measurements were carried out using electrochemical and surface techniques. Potentiodynamic polarization curves suggested that this compound was an effective corrosion inhibitor for mild steel and the protection efficiency was increased with the increase in inhibitor concentration. The experimental results indicated that this organic compound was a mixed-type inhibitor. Adsorption on the mild steel surface followed the Langmuir isotherm model. Activation parameters and thermodynamic adsorption parameters of the corrosion process such as Ea , ΔH, ΔS, Kads, and ΔGads were calculated at different temperatures.