A cobalt hexacyanoferrate (CoHCF) modified glassy carbon (CoHCF/GC) electrode was prepared electrochemically. The voltammetric responses of CoHCF are stable and the electrochemical behaviour is related to the concentrations of supporting electrolyte and counterions. The CoHCF/GC electrode shows electrocatalytic activity toward the oxidation of ascorbic acid in phosphate buffer solution. The electrocatalytic rate constant of the CoHCF/GC electrode for the oxidation of ascorbic acid is determined using rotating disk electrode measurements.