Three thiadiazole derivatives, namely 5-phenyl-2-amino-1,3,4-thiadiazloe (APT), 5-(4-methoxyphenyl)-2-amino-1,3,4-thiadiazloe (AMPT) and 5-(4-nitrophenyl)-2-amino-1,3,4-thiadiazloe (ANFT), have been synthesized as new inhibitors for the copper corrosion in 0.5 M H2SO4. The inhibition properties of the inhibitors were studied by means of potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements. The results show that the order of inhibition efficiency is AMPT > APT > ANPT. The values of free energies of adsorption, as calculated from the Langmuir adsorption isotherm, indicate that the thiadiazole compounds adsorb on copper by a physisorption mechanism in 0.5 M H2SO4. The correlation between inhibition efficiency and quantum chemical parameters has been investigated by PM3 quantum chemical calculation. (C) 2009 Elsevier B.V. All rights reserved.