Electrochemical quartz crystal microbalance combined with cyclic voltammetry was used to study the electrodeposition of PbS thin-films on Au surface. The electrodeposition was carried out by cycling between two potentials with voltage scan rates of 0.1 and 0.01 V/s. In addition, the electrochemical behaviour of PbS film and the related precursors, PbEDTA(2-) and HS- were studied separately. It was found that the reduction of PbEDTA(2-) occurred at a more positive potential on the PbS surface than on the Au surface. Similarly, HS- oxidised at a more negative potential on the PbS than on the Au surface. Therefore, the deposition of PbS was proposed to occur by two mechanisms. The first mechanism includes the reduction of PbEDTA(2-) to elemental lead which during the oxidation reacts with HS-. In the other mechanism, PbS surface induces the chemical reaction between PbEDTA(2-) and HS. The electrodeposited PbS is stable in the potential range of -1.2 to -0.2 V vs. Ag/AgCl,