Effect of 2,5-dimercapto-1,3,4-thiadiazole (DMTD) concentration on the electrochemical behaviour of bronze was studied in 30g L-1 sodium chloride (NaCl) by means of surface analyses and electrochemical techniques. Scanning electron microscopy (SEM) was used to observe surface morphology. Raman micro-spectroscopy was carried out to study chemical structure of deposited layers. X-ray photoelectron spectroscopy enabled elemental characterization as well as molecular structure investigation. Finally, electrochemical polarization and impedance permitted a thorough study of corrosion protection behaviour reached through the presence of DMTD-based organic layers on the surface. Above 1mM, a fast adsorption of DMTD on copper (Cu) and lead (Pb) allows a thin and blocking film to be formed on bronze surface. DMTD prevents oxide formation at high concentrations, and the surface film is mainly composed of Cu-I-DMTD and Cu-II-DMTD complexes as evidenced by spectroscopic techniques, with a bidentate adsorption at 1mM and monodentate adsorption at 10mM. [GRAPHICS] .