Acetyl thiourea chitosan polymer (ATUCS) has been synthesized and evaluated as corrosion inhibitor. The electrochemical behavior of mild steel in naturally aerated 0 5 M H2SO4 acid containing different concentrations of ATUCS has been studied by potentiodynamic polarization. electrochemical impedance spectroscopy (EIS) measurements and surface examination via scanning electron microscope (SEM) technique. The results of EIS showed that the resistance (R-t) increases slightly with increasing immersion time indicating a slight decrease in corrosion rate of the steel with time. Also. the corrosion rate increases with either increasing temperature or decreasing the polymer concentration as observed by polarization technique Electrochemical impedance spectroscopy measurements under open-circuit conditions confirmed well polarization results ATUCS has shown very good inhibition efficiency (IE) in 0.5 M sulphuric acid solution reaches to 94.5% for 0 76 mM concentration IE of this compound has been found to vary with the concentration of the polymer solution, immersion time and temperature. Published by Elsevier Ltd