The electrochemical reduction of oxygen has been studied on multi-walled carbon nanotubes (MWCNTs) modified highly oriented pyrolytic graphite (HOPG) electrodes in 0.1 M KOH solution using the rotating disk electrode (RDE) technique. The oxygen reduction behaviour of MWCNTs/HOPG electrodes of various modifications was compared. Electrochemical studies indicate that the MWCNTs/HOPG electrodes show a remarkable electrocatalytic activity towards O-2 reduction in alkaline media. The number of electrons transferred per O-2 molecule was a function of potential and it increased up to four at high negative potentials. The O-2 reduction behaviour of MWCNTs/HOPG electrodes using oxidatively treated MWCNTs was also studied. The oxidative pre-treatment of MWCNTs did not change their electrocatalytic properties for oxygen reduction in alkaline solution to a noticeable degree. (c) 2006 Elsevier B.V. All rights reserved.