Cathodic dioxygen (O-2) reduction was performed at a modified glassy carbon electrode (GCE) by single-walled carbon nanotubes (SWCNT)/Nafion (R)(NF) film with cobalt (II) tetra (2-amino-phenyl) porphyrin (CoTAPP) and palladium (Pd) nanoparticles incorporated and employed as doping agents. Both the electrochemical behavior of SWCNT with a P(CoTAPP)-Pd nanoparticle matrix and the electrocatalytic reduction of O-2 were investigated using transmission electron microscopy (TEM), cyclic voltammetry (CV) and rotating ring-disk electrode (RRDE) techniques in 0.1 mol l(-1) H2SO4 aqueous solutions. The electrocatalytic reduction of O-2 at the SWCNT/NF/P(CoTAPP)-Pd composite film established a pathway of four-electron transfer reductions into H2O. Hydrodynamic voltammetry revealed that the modified electrode was catalyzed effectively by the four-electron transferred reduction of dioxygen into H2O with minimal generation of H2O2. The SWCNT/NF/P(CoTAPP)-Pd composite film showed a highly efficient electrocatalytic performance. P(CoTAPP)-Pd was an effective mediator for the reduction of dioxygen and was responsible for the enhanced catalytic activity. (C) 2011 Elsevier Ltd. All rights reserved.