The adsorption process of the redox-active self-assembling molecule [Os(bpy)(2)(py=py)Cl](+) (bpy = 2,2’-bipyridine and (py=py) = trans-1,2-bis(4-pyridyl)ethylene) onto a Pt electrode has been investigated in aqueous KClO4, KPF6, and KNO3 electrolyte solutions using the quartz crystal microbalance in conjunction with cyclic voltammetry. In all the electrolyte solutions examined, the adsorption of the Os complex appears to be accompanied by water molecules, whose number is higher in KPF6 solution (38-41) than in KClO4 (26-34). In KNO3 solutions the hydration number increases with increasing surface coverage of the Os complex. The mass transfer during the redox reaction of the adsorbed Os complex monolayer is of the anion exchange type in all the electrolyte solutions examined. Further, it was determined that the anions are accompanied by water molecules, whose numbers (for surfaces at saturation coverage of the Os complex) in a KPF6 solution (6-7) were higher than in the other electrolyte solutions. At surface coverage values below saturation, only 0-0.5 water molecules accompany the anions. Additionally, we also demonstrate that the film properties do not change during the self-assembly or redox processes of the Os complex, as determined by means of admittance measurements of the quartz crystal resonator on the basis of the electrical equivalent circuit.