Carbon black supported ultra-high loading silver nanoparticle catalyst (Ag/C) was prepared by a modified ethylene glycol reduction method. The thermogravimetry analysis showed that the Ag mass loading of this catalyst reached up to 392 wt.%. The X-ray diffraction and scanning electron microscopy characterizations showed that the Ag nanoparticles were ca. 10 nm diameter of fine spheres with a face-centered cubic crystal structure, and were densely stacked but not aggregated on the carbon black surface in spite of such ultra-high loading and small size. The chronoamperometry and polarization studies utilizing rotating disk electrode (RDE) or rotating ring disk electrode (RRDE) revealed that this ultra-high loading 392 wt.% Ag/C catalyst exhibited higher electrocatalytic activity for oxygen reduction reaction (ORR) in alkaline medium. The ORR proceeded a four-electron process when compared with the low loading 40 wt.% Ag/C catalyst. Furthermore, the chronopotentiometry test on gas-diffusion electrode containing the 392 wt.% Ag/C catalyst implied that this catalyst had a considerably stable ORR activity for application in brine electrolysis. (C) 2013 Elsevier B.V. All rights reserved.