The effect of a new corrosion inhibitor namely, N-(5,6-diphenyl-4,5-dihydro-[1,2,4]triazin-3-yl)-guanidine (NTG) has been synthesized and its inhibitive performance towards the corrosion of copper in neutral solution of 3% NaCl has been investigated. Corrosion inhibition was studied by chemical method (weight loss) and electrochemical techniques including potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and electrochemical frequency modulation (EFM). These studies have shown that NTG was a very good inhibitor and the inhibition efficiency up to 99% in 3% NaCl is obtained. Data obtained from EIS were analyzed to model the corrosion inhibition process through equivalent circuit. Comparable results were obtained by different chemical and electrochemical methods used. The adsorption of the inhibitor on the copper surface in the acid solution was found to obey Langmuir's adsorption isotherm. (C) 2008 Elsevier B.V. All rights reserved.