Osmium oxide/hexacyanoruthenate films have been prepared using repeated cyclic voltammetry, and their electrocatalytic properties have been investigated. The osmium oxide/hexacyanoruthenate films were deposited directly from mixed Os3+ and Ru ( CN ) 6 4 - ions in a pH 2 solution. Electrochemical quartz crystal microbalance (EQCM), cyclic voltammetry, and UV–visible spectroscopy were used to study the growth mechanism of the osmium oxide/hexacyanoruthenate films. The EQCM data indicated that the redox process was confined to the immobilized osmium oxide/hexacyanoruthenate film, which showed a single redox couple with a formal proton-dependent potential at 0.35V. The electrocatalytic oxidation of dopamine, epinephrine, and norepinephrine and S 2 O 3 2 - and SO 5 2 - by the osmium oxide/hexacyanoruthenate films was studied. The electrocatalytic reactions of the osmium oxide/hexacyanoruthenate films were also investigated by the rotating ring-disk electrode method.