The investigation of the extract of various plants (Prunus cerasus (PC), Cypress sempervirens (CS) and Terminalia catappa (TC) leaf was investigated as corrosion inhibitor of mild steel in 0.5M HCl ,2M HCl and 0.5M H2SO4 using electrochemical polarization , electrochemical impedance spectroscopy and FTIR spectroscopic analysis. The thesis consists of three chapters. Chapter I is the introduction, Chapter II represents the experimental techniques, and Chapter III contains the results and their discussion. In the first chapter an introduction was given which deals with the corrosion and its inhibition, literature survey of the inhibition of steel corrosion in acid solutions using plant leaf extract and the aim of the work. Chapter two showed the experimental techniques used in the investigation. The third chapter showed the obtained results and their discussion. The results indicate that leaf extracts exhibit good inhibition characteristics to corrosion on mild steel. The polarization curves show that PC, CS and TC leaf extracts act as mixed type inhibitors with predominant cathodic character in 2M HCl. It was found that the addition of the plants' leaf extracts causes an increase in the charge transfer resistance where Cdl in μF. These indicate adsorption of the leaf extracts on the mild steel surface and formation of a barrier for the metal to diffuse out to the bulk. The activation parameters (Ea, ΔH*and ΔS*) were calculated in absence and presence of different concentrations of the leaf extracts. Adsorption isotherms (Langmuir, kinetic - thermodynamic, Flory-Huggins and Temkin models) applied to the polarization results of PC, CS and TC leaf extracts. The values of binding constants obtained from the kinetic–thermodynamic model suggested that the inhibition efficiency of different plant leaf extracts could be arranged in 0.5M HCl and 2M HCl in the order: Prunus cerasus > Cypress sempervirens > Terminalia catappa while in 0.5M H2SO4 they follow the order: Cypress sempervirens > Prunus cerasus > Terminalia catappa Based on FTIR analysis and extensive literature survey, linalool was chosen as selected active chemical constituent for Prunus cerasus and Cypress sempervirens leaf extracts to be tested as corrosion inhibitors. Evaluation of potential of zero charge PZC indicated that the steel surface is negatively charged in 0.5M HCl and 0.5M H2SO4.While the surface charge metal is neutral in 2M HCl indicating that none of ions adsorb on the surface of metal through their ionic center.