Combination of polyoxometallate-modified multi-walled carbon nanotubes, cobalt porphyrin, and peroxidase (horseradish, cabbage) enzyme within the film (deposited on glassy carbon) produces a bio-electrocatalytic system capable of effective reduction of oxygen in neutral media such as 0.1 mol dm-3 KCl and 0.1 mol dm-3 KCl + 0.01 citrate buffer (pH=6). An important function of carbon nanotubes is to improve transport of electrons within the film. Co-deposition of the peroxidase enzyme together with the cobalt porphyrin catalytic centers leads to bifunctional synergistic effect that is evident from sizeable positive shift of the oxygen reduction potentials and significant increase of voltammetric currents. The bio- electrocatalytic system also exhibits relatively much higher reductive activity towards hydrogen peroxide. It is reasonable to expect that the reduction of oxygen is initiated at cobalt porphyrin redox centers, and the undesirable hydro gen peroxide intermediate is further reduced at the horseradish or cabbage peroxidase enzymatic sites.