Catalase (Ct) was modified using Woodward's reagent K (WRK) as a specific modifier of carboxyl residues. The modified Ct was immobilized on an oxidatively activated glassy carbon electrode surface to investigate its direct electrochemistry. Using cyclic voltammetry an irreversible reduction peak was obtained at approximately-0.362 V vs. Ag/AgCl in buffer solution, pH 7, and at a scan rate of 0.1 V s(-1). The electrochemical parameters, including charge-transfer coefficient (0.27), apparent heterogeneous electron transfer rate constant (13.51 +/- 0.42 s(-1)) and formal potential of the Ct film (-0.275 V) were determined. The prepared enzyme electrode exhibited a response to H2O2.