Effect of 2,5-dimercapto-1,3,4-thiadiazole (DMTD) concentration on the electrochemical behaviour of bronze was studied in 30 g 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 (XPS) 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 1 mM, 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 1 mM and monodentate adsorption at 10 mM.