5-(Phenyl)-4H-1,2,4-triazole-3-thiol (PTAT) was synthesized and tested as a corrosion inhibitor for copper in stagnant and stirred 3.5% NaCl solutions using potentiodynamic polarization, potentiostatic current time, weight loss and pH measurements along with Fourier transform infrared spectroscopy (FT-IR) investigation. Potentiodynamic polarization measurements indicated that the presence of PTAT in both stagnant and stirred solutions decreases cathodic, anodic and corrosion currents, polarization resistance and corrosion rate and this effect increases greatly when the measurements were carried out after 100h immersion of the copper electrode in the test solutions. Potentiostatic current time measurements also showed that the PTAT molecules are significantly decreasing the values of current with time due to the strong adsorption of PTAT onto the copper surface. The inhibition efficiency of 500ppm PTAT obtained by weight loss measurements is about 73%, increasing to about 90% at its concentration of 1500 ppm, as well as, the accompanied pH values were noticed to decrease with the presence of PATA and the increase of its concentrations. FT-IR investigation revealed that PTAT molecules are adsorbed strongly on the copper surface at an open-circuit potential. Results together are in good agreement and showed clearly that PTAT is a good mixed-type inhibitor for copper corrosion in 3.5% NaCl solutions. (c) 2006 Elsevier B.V. All rights reserved.