Polynuclear mixed-valent films of ruthenium oxide/hexacyanoferrate ( RuO / Fe ( CN ) 6 3 - ) and ruthenium hexacyanoferrate (RuHCF) have been prepared using repetitive cyclic voltammetry. The deposition process and the films’ electrocatalytic properties in electrolytes containing various cations have been investigated. The cyclic voltammograms recorded the deposition of the mixed ruthenium oxide/hexacyanoferrate and ruthenium hexacyanoferrate films directly from the mixing of Ru3+ and Fe ( CN ) 6 3 - ions from the acidic aqueous solutions containing various anions. The electrochemical quartz crystal microbalance, cyclic voltammetry, and UV–Vis spectroscopy were used to study the growth mechanism of the mixed ruthenium oxide/hexacyanoferrate and ruthenium hexacyanoferrate films. The mixed ruthenium oxide/hexacyanoferrate and ruthenium hexacyanoferrate films exhibited four redox couples with formal potentials that demonstrated a proton effect in acidic aqueous solution and an anion effect. The electrochemical quartz crystal microbalance results indicated that the redox process was confined to the immobilized mixed ruthenium oxide/hexacyanoferrate and ruthenium hexacyanoferrate film. Electrocatalytic reactions of dopamine, epinephrine, norepinephrine, S 2 O 8 2 - , and SO 5 2 - were carried out by the mixed ruthenium oxide/hexacyanoferrate and ruthenium hexacyanoferrate films. The electrocatalytic oxidation of ethyl alcohol, isopropyl alcohol, l-cysteine, and ascorbic acid by the mixed ruthenium oxide/hexacyanoferrate and ruthenium hexacyanoferrate films too was investigated.