The electrochemical behaviour of glassy carbon/polyaniline (GC/PANI) and GC/PANI/Pt electrodes for oxygen reduction in buffered neutral aqueous solutions was investigated to determine the function of PANI in the composite electrodes. It was found that PANI exhibited little electrocatalytic activity for oxygen reduction in neutral solutions because of its poor conductivity. However, for oxygen reduction the presence of PANI in both GC/PANI and GC/PANI/Pt electrodes could inhibit the diffusion of O2 through the polymer matrix to level out the effect of non-uniform distribution of active sites so that a flat current plateau could be obtained even when the electrodes were rotated. It is concluded that PANI is a promising sensor material for the measurement of dissolved oxygen in neutral solutions despite its poor conductivity.