A stable electroactive thin film of cobalt hexacyanoferrate (CoHCF) was electrochemically deposited on the surface of a microband gold electrode. The cyclic voltammograms of CoHCF film indicate the presence of two redox peaks corresponding to the hexacyanoferrate(II/III) redox couple. The electrochemical behaviour of CoHCF is related to the concentration of supporting electrolyte and counter-ions. The modified electrode shows excellent electrocatalytic activity towards the oxidation of reduced nicotinamide adenine dinucleotide (NADH) in phosphate buffer solution (pH 7.0), with an overpotential ca.310-370 mV lower than that of the bare microband cold electrode. The catalytic peak current is proportional to NADH concentration in the range 0.5-6.0 mM with a correlation coefficient of 0.98. The catalytic rate constant of the modified electrode for the oxidation of NADH is determined using a rotating-disc electrode. The mechanism of the oxidation of NADH catalysed by the electrode is discussed.