The inhibiting action of N-(5,6-diphenyl-4,5-dihydro-[1,2,4] triazin-3-yl)-guanidine (NTG) on the corrosion of copper in 0.5 M sulphuric acid was studied. NTG was synthesized and studied as an inhibitor for corrosion of copper. Results of weight loss, potentiodynamic polarization and electrochemical impedance (EIS) measurements consistently identify NTG as a good copper corrosion inhibitor. Potentiodynamic polarization studies clearly showed that NTG is a cathodic-type inhibitor for copper in 0.5 M H2SO4 solutions. Data obtained from EIS were analyzed to model the corrosion inhibition process through an equivalent circuit. The adsorptive behaviour of NTG on copper in 0.5 M H2SO4 was also investigated. The copper/NTG/solvent interfaces were simulated and the charges on NTG molecule as well as its structural parameters were calculated in presence of solvent effects. Adsorption of NTG on the surface of copper is found to obey the Langmuir adsorption isotherm. (C) 2008 Elsevier B. V. All rights reserved.