The inhibition of copper corrosion by 1,3,4-thiadiazole-2,5-dithiol (bismuthiol), under 0.5 M HCl at 25 C, was studied by means of the potentiodynamic polarization technique. It was found that bismuthiol was chemically adsorbed on the copper surface, and follows a Langmuir isotherm. The inhibition mechanism was found to be mixed, and it was originated through the formation of bismutiol-copper complexes on the surface of the metal. Bismuthiol shows good inhibition efficiency under these conditions